In my opinion, you are the authority on that. I do not think it is too generous (I am similarly generous), but i know that I am setting the bar with my encounters. The main question to ask is whether or not you're using monsters straight out of the MM, or tailoring them to be more difficult. If so, it may be that you need to "up the ante", and consider the PCs one level higher for CRs. That is, if you use CR to determine experience; I don't. I level the PCs at story-relevant points.
Go with it. :)
You can modify the effective abilities of later NPC Opponents if the players appear to be having too easy of a time of it.
18 10 10 11 14 17
Point buy wise, thats 16, 2, 2, 3, 6, and 13, for a grand total of 42 points.
Definitely higher than the 32 heroic point buy. It is the general consensus that 10 points above is fairly equivalent to a +1 level adjustment.
However, consider that SCAP is a brutal AP, one of the meanest, and is known for being rather....sketchy on treasure rewards. Your higher point buy might give them the edge needed to survive the initial adventures, and the staying power to survive the latter ones.
If you wanted to keep the point buy more like the 32 heroic set, you could change your "lowest becomes an 18" to "lowest becomes a 16" or even "14". The 16 version would reduce the total by 6, and the 14 version would reduce it by 10. Just depends on if you want the "replace lowest" function to give them a "awesome" stat for primary scores, "great" for primary or secondary, or a "good" stat for shoring up any weaknesses.
Overall, I think this will work fine for you, as long as you are aware of the nature of the SCAP itself, and of what your players can do with these stats.
Just my 2cp.
My suggestion would be: Let them have the 18.
I'm currently in a SCAP-Campaign with a fixed array:
17 16 14 13 10 8 (point buy would be 36)
Currently we're scraping through, with the occassional death (about one dead character every two sessions, in average). I don't think a point buy of 42 would be too bad for this adventure path.
I upped the power level on my group by allowing them 42 points for gestalt characters. I thought I was only going to have 2 players and I ended up with 4, not sure how that happened but it has been fine so far. I haven't changed the power level of the encounters at all and the group has been suitably challenged. No one has died but there have been some close calls so far. That is mostly because the healer (elven druid/paladin) insists on being a front line fighter instead of a support healer for the two warriors (dwarf barbarian/monk and ogre barbarian/ranger). The other is the party leader and acts as a support spellslinger and rogue appropriately (drow sorcerer/rogue).
Once you get into it I think you'll see that the higher stat is not enough to blow the power curve of the encounters. If my group is still challenged then I am sure yours will be as well.
My group had a 30 point buy and I also only have 5 PC's. So far the party have made it through without any deaths. They are almost at the end of Drakthar's Way so there is still a long way to go.
Last session is probably the closest I've come to killing a PC (and probably not that far from a TPK) with 2 PC's knocked into the negatives in the one combat.
I think the power level will depend on what non-PHB books you give them access to. My players have access to most of the WotC splatbooks. As a result they are probably a little more powerful than PHB-only PC's.
Olaf the Stout
I don't see anything wrong with giving them an 18 in place of their lowest score, particularly since the scores are rolled. And if a PC gets a really good bump from it, it's not that big a deal.
By the way, ever played MERP or part of the Rolemaster family? Because in that game you also replaced your lowest score with a high value. I always thought it was kind of a cool mechanic.
I think the power level will depend on what non-PHB books you give them access to. My players have access to most of the WotC splatbooks. As a result they are probably a little more powerful than PHB-only PC's.
I think Olaf hit the nail on the head with what i quoted above.
I run the SCAP for 6 players, all rolled stats, and all are core rulebook characters. I did alter the healing and spell memorization rules, which makes the party more flexible and long lasting than by the book. So far, only one death. We are currently at the start of Test of the Smoking Eye.
I think that non-core sources and house rules will have a much bigger effect on your game than high stats. I wouldn't worry about it, unless of course you're using high stats in addition to non-core rules.
It's a great series of adventures, and very challenging in places. Enjoy!
My 'rule of thumb' feeling on this is your adding about +1 to a PCs LA for a point buy thats above 28. I'd probably call it +2 after 38.
Your adding about another +1 if you have a lot of splat books in play.
I'd be somewhat leery of the combo however because your going to get the character that finds the magic item or ability thats based on the stat modifier and its somewhat dangerous if you have something like a Paladin with Eleven Smite Evils a day (true story - I have one of those at my table).
I don't think it's TOO generous (although it is QUITE generous). My only objection comes from the Player's standpoint. Some Players are going to benefit a LOT more from your gift than others, and that's not fair to the ones who benefit less.
But then, I made the decision years ago to go with point buy, the only system that starts characters off on completely fair and equal footing. I don't know about you, but I always used to seem to have at least one Player, if not more, who came in with a couple of 18's and nothing below a 12 or 13. I have never liked the rolling dice method UNLESS I was there personally to see the rolls being made. Even then, I kept a set of house rules with fairly generous "unplayable" exceptions that would allow the dice to be re-rolled if the scores did not meet some minimal acceptable standard.
All that said, I certainly don't think your ruling is bad. What you have read is true. My party is about halfway through Demonskar Legacy, and it has been a very rough road! A little extra oomph is probably going to do no more than make the PCs more likely to survive -- I honestly don't think you need to worry whatsoever about them being unbablanced.