If you're keeping the bike stock, I'm proud of you they are great looking bikes, otherwise shedding a bunch of weight helps.
Often it's said there's nothing like a displacement increase, standard 750 pistons with some machining is an option. (some of these "kits" on E-bay come with rings that are JUNK) but like mlinder says a different cam is noticable and inexpensive.
At least do a good valve job at the same time.
Replacing the stock air filter with Uni in the original airbox breathes a bit better and will require raising the needle and a possible bump in main jet.
moham can tell you what it costs to go-big, depends on how deep your pockets are.
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