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I was trying to make a magic trap for an adventure, and I hit a few snags.
1. I can't find what the bonus for a ranged touch spell should be, but if I look at the examples I'm guessing it's equal to the spell level. Is that correct?
2. Mechanical traps have a +1 modifier to CR if they have an automatic reset, but magical traps don't? Is that correct?
Short answer: It's entirely up to the GM.
Long answer: It doesn't actually say this in the rules, but Ranged Touch Spell traps *should* generally have a minimum Attack bonus equal to the Spell Level (which can increase with Metamagic). So if you're making an Acid Arrow Trap with no metamagic, it would have a +2 to the attack roll because it's a level 2 spell. Likewise, if you Empowered a Scorching Ray trap to lvl 4 spell slot, then it would have a +4 ranged touch attack, etc.
However, it DOES say in the rules that the BUILDER of the trap sets the Attack Bonus, so honestly you can set it at whatever you want (without following the minimum spell lvl x1 pattern). Magical Trap DC's are typically 10 + (Spell level x 1.5), so if you want to crank up the Attack bonus for a particular magic trap, having a ranged touch attack equal to Spell Level x 1.5 is also perfectly acceptable. It also says in the rules that Magical Traps generally do not reset because you cast the spell when you make the trap, but this can also be GM-waived if you want too; you ARE the GM after all. For example, Permanency on a Wall of Fire spell will reset after 10 minutes if its dispelled <--- and that's perfectly legal. If you want to GM-waive an Acid Arrow Trap into resetting every round, that's fine too, but that's a homebrew trap.
So it's entirely up to the GM to set the Trap's Attack bonus and whether it resets or not. Generally speaking, 1x to 1.5x Spell Level is a good range for a Ranged Attack Bonus. But if your PC's have been casting the spell Poke the GM as of late, set that baby at 2x to 3x Spell Level for maximum cryface :)
People guard their most treasured possessions and protect their most secret venues with Traps, and they're not trying to take 4th place in a Tickling Competition. So remember that Traps are designed to kill, maim, and/or capture, so use them ruthlessly and set your Attack Bonuses and DC's accordingly.
As a GM, I think Quality > Quantity when it comes to trap-making. I generally consider a Trap to be equivalent to a Boss Fight in terms of how much damage I'm willing to put out upon the party. And if they survive, they should be limping. So personally, I don't usually use generic magic traps very often. If you want to make your own custom traps, you should check out Grimtooth's Traps. It's a great resource to get some inspiration and get the imagination juice flowing for making your own custom traps. Even though they go through a small slice of hell, it really does create a memorable experience for your PC's, and it gives them a significant sense of achievement for besting it.
It's the difference of "hey remember when we had that Flying Vorpal Axe trap with the crumbling floor with the electrified walls over that Spike Pit while the room was being flooded with poison that we did a few years ago?" vs. "hey remember when we had that Empowered Scorching Ray trap we did a few years ago?"