When building my lvl 8 Alchemist, I felt like this character was supposed to be an extremely versatile character that could fit whatever role was needed depending on what the scenario dictated. That said, once I actually played the class, I found the Alchemist somewhat lacking and ineffectual. Problems I had: although the poison would imply that the character should be somewhat melee focused, the alchemist is only proficient in simple weapons. Giving the class some martial weapons (similar to a rogue's) would not imbalance the class, I dont think.
Relying on bombs felt somewhat...ineffective. I wish there was a way to improve a bomb focused alchemist's ability with thrown weapons (larger range increments, OR just trying to hit the square's touch AC, instead of a specific character's). I, honestly, was very disappointed with how FEW decisions I had to make when designing my character. I wish the Alchemist would get less "static" abilities, like the poison stuff, and instead just make more discovery choices (so, adjust a lot of the abilities all alchemist gain to discoveries they can make at more regular intervals, every even level like a rogue sounds right to me).
The biggest issue I had was that, the bomb ability aside, I didnt feel like the Alchemist was any better of an Alchemist than a player would be. Sure, you get an increased Craft: Alchemy check, but that wasnt that significant of a benefit---with the exception of a random skill check, I felt like that benefit was more flavor than anything. One option is to have the alchemical devices (alchemist's fire, tanglefoot bags, etc) work better than a regular PCs stuff.
The option I much prefer, though, is to grant the Alchemist more versatility. The option I like is to give the Alchemist an ability similar to the Pathfinder Chronicler's Deep Pockets. There are definitely cases where the ability to spend a full-round action to find a tanglefoot bag could change the game, and these are the cases that would justify bringing an alchemist over other classes, in my opinion.