Not really, they don't outperform a good stock carb setup, make your legs smell like gas, and cost a ton of money. And from what I've seen have lots of other annoying side effects. Like no choke so cold starting is a PITA, and when it gets hot in traffic it runs like crap.
What flat-slides did you have and perhaps you could also elaborate on what the 'lots of other annoying side effects' are?
What you say is not my experience - The Mikuni TDMR's that I run don't smell (they are down-draft), has a choke and is fuels well all through the rev range and are quite happy in town.
They also have accelerator pumps which gives
instant go when you wind the throttle.
They certainly gave more power than my standard set-up but I do concede that could probably have been improved upon.
I would also suggest that they are a good idea if you increase the capacity of the motor.
Regarding NOS - cheap(ish) power and fine if you are dragging the bike but given the short time the gas lasts I wonder how practical it is for road use?
I don't think there is a 'cheap' way to improve the performance of an engine - if there was then manufacturers would have Incorporated it.
If you want Gen II performance then having a motor with a similar displacement (ya can't beat cubes!) would be my first choice....then carbs...then cams....then head job.... - not cheap.
It would be prudent to also upgrade brakes and suspension to handle all the extra go.
Bottom like is that you are talking big bucks.
I think the most practical suggestion made so far has been to get a Gen II - I suspect it would work out as the cheapest option in the long run.