I guess I'm on the opposite end of this spectrum. I've played a lot of games as tiny evil and only had a problem building up a huge ap amount once, which was due to my team not doing well and my being unable to keep up with enemy champions because of it. I also like the Q skill just as it is. It's noticably less powerful than other similar nukes (annie's disintegrate and ryze's Q skill come to mind), but it creates an interesting choice for the player. Do I try to nuke champions down with it, or use it on creeps to gain ap? Do I try to kill a champion with my R skill for the mana return or the Q skill for the 5 ap?
My general strategy with him is to get a meki pendant early for mp5, and try to kill creeps with the q skill whenever possible, obviously getting it first. Then I level my Q skill whenever I can to make it easier to kill creeps with it, as well as to make it a nuke strong enough to really have an impact. I generally get one point in his aoe stun-prison early, and then put the rest into meteor, though either the prison or meteor could be leveled first depending on matchups, etc.
Tiny evil really shines when you get 3-4 points in meteor and a respectable amount of ap, say 60. By this point you should be able to take out 3+ creeps at a time with a meteor, and any that don't die immediately are easy pickings for an attack kill or Q kill. I usually make a philosopher's stone ASAP to be able to stay in my lane and basically continually cast Q for AP. After that comes boots to sorcerers/swiftness (usually sorcerers) and then the +70 ap and +10 ap per hero kill item. This allows me to potentially gain 15 AP from killing a hero with a Q. I've also seens an early tears of the goddess to shear build work very well, and shear is certainly an item to prioritize since it works very well on tiny.
Typically by the time I reach level 18 in a game with tiny evil I'm at approximately 250-300 ap and have gotten some cd reducing items to allow me to cast Q every 3-3.5 seconds, meteor every 10 seconds, the aoe prison-stun every 15 seconds, and the R ultimate every 60 seconds (these are just my rough guesses from memory, but it works out to something like that). At this point evil can stop pushes cold with meteor, chase down heroes well with his prison, and against any champion with a significant mp base simply cast a prison-attempted meteor-R cast-Q cast for the kill. Or do a Q rundown, which is running next to the hero you're trying to kill and only stopping to do quick casts of Q, and prison when it's up. I generally do around 10-1 with this strategy, with one notable time having me go 14-0 with some assists as well.
ASIDE FROM THAT MASSIVE BLOCK O'TEXT: I like the passive as it is. it can be useful when laning early to give an extra jolt to your spells, and reduce their spell power. One thing to note when using it is it will only have an effect on champions, and only champions with some ability power. Also if you hit a champion with 2 AP for example you should only get 2 ap yourself, and that champion loses his 2 ap. Putting the AP leach on the Q spell would incentivize people to cast it on champions too much for my liking, and try to last hit creeps with normal attacks which is generally much more diffficult (attack is slower to arrive and weaker than a Q spell). My only real advice is to not worry about getting a fat stack of ap boosts before casting your spells, and just cast and attack normally. I'd compare waiting for a lot of stacks pre-cast to an ashe that always waits 15 seconds between attacks to make sure her crit chance is maxed for her next attack, it's just not the best way to go about it.
Anyway that's all I have to say about tiny evil (for now), he's definitely one of my favorite champions and also one of the ones I hate seeing on the other team the most! Thanks for taking the time to read this extra-long post, and I'll see you in the beta!