Hot rodding a vintage bike never pays off financially. Those who seek a vintage, don't generally seek modified. Maybe a few out there, but the investment is not rewarded.
There's little gain to swapping to modern electronics if the stock products still work. If you are undertaking a major customization, re-wire, re-location of everything, then a modern solid state R/R is convenient and easy enough to swap over.
Buchanan's aluminum Sun rims and their stainless spokes are hugely popular. Much lighter rims, varying widths and diameters, and the stainless spokes are nicely corrosion resistant. The 550 will handle up to a 150 rear tire on a 4.25" rim, but you need to check carefully that you don't require an offset sprocket. Wider tires will definitely require a sprocket offset.
A 650 motor swap into your bike is probably the easiest performance gain for the money. Better head, has the cam, you lose the kickstarter. Electronics/harness needs some fiddling too. Some are doing this swap now, and have swapped out the 650 ignition to aftermarkets to abandon the stock, trouble-prone units.
A properly maintained stock swing arm, good bushings, and quality rear shocks will make your bike fell nimble, stable, and tight. There's also new drum-disc conversions so you can run modern brakes on your 550, paired with modern quality, yet stock forks on the front. Or, modern fork swaps up front for better handling and braking. Its all out there. But money spent on suspension and braking makes the best return and most enjoyment despite HP mods.
Its more fun to ride a slow bike fast, than a fast bike slow.
