Similar boat, I decided to run the 7 cluster to death, when I build a new wheel, I'll put in an 8, not 9 ( don't ask ) The upgrade involves derailler, shifter, chain and possibly the chainrings tho- I did run IG 7 spd chain onto HG 9 spd chainrings fine.
The 7 speed rapid fires are harder to find..most mechanics got a bag somewhere.
I would suggest the money might be better spent on lightness or whatever upgrades.
Some Fisher bikes are super nice, and worth upgrading.
How are your tires\rims\seat\pedals\grips? All these thing contribite to the 'feel' of the ride.