nice ideas, I like some of them more than others. There is one I would like to object against and that is the power-up of towers by GP or prices from nathor.
If that is executed, the whole tournament idea of this site would difficult to understand.
Let me explain.
Take for example an power-up pellet tower for the same cost that shoots 10% faster. Currently you need to have 10 pellets to kill the first wave of grouped creeps; with the power-up ones you would only need nine. Anyone spending GP to see how a torunament is played the best would be extremly annoyed in erplaying the opening - as he has no power-ups.

I like the idea of towers that insltantly kill, or the teleport back to the start one too.

An idea to further the instant death tower. Each tower has 5 upgrades to make it to the top level, so with this tower, make it fire, say every 10 secs, and make a lev 1 tower take 50% of the creeps health. Upgrades should be pricey, and add 10% to the damage it takes, making it max out at 100% for a fully upped tower.

The teleport tower would be good too, cant thiink of anthing that would be better actually, would be great for those annoying creeps that seem to sneak past your defences.

like i said, an greatly placed insta kill tower can take out the 4 boss, no?

Ya, insta-kill towers might not be the best idea. If used properly they could be really cheap.

Hey,
what is with a suicide Tower. It will be cheap and kill only one creep AND itself. But it has only range 1.

good ideas!

i'd like a kamikaze powerup. it randomly chooses a creep on the map, witch starts running (to biggest crowd in a certain dist?) and explodes, dealing damage scaled by its max hp in a certain radius.
if the creep is the strongest on the map -> small radius
if it's the weakest -> whole map affected

there are several parameters to tweak: percentage of the creeps infected/random direction and distance running, or simply killing all creeps in the way while running for 2 sec, etc...

I like the frost volcano (call it a molasses tank?) idea, the laser wire (though there'd have to be a limit, otherwise you eventually get a spider web of lasers), and the kamikaze is great and unique.

What about a "mutant tower", that changes creeps from one type to another? Maybe 90% of the time it changes it to an easier creep (something slower / fewer HPs / etc.), but maybe there's a chance of it changing a creep to a worse foe.