1. Adding more cogs does not necessarily add more utility. It may primarily only add smaller cogs (higher gears) than you have now. On an older bike that may have a 52 tooth chainring that is of little value

2. Adding more rear cogs will be costly - 9 speed will require chain, , wheel, cassette and brifters and possibly derailleur

3. As noted above spokes that are too long can be ground down, but irrelevant if you decide to replace the wheel for the upgrade.

4. Look up "chainline" and check to see if your chainwheels are in the proper place. Replacing the derailleur may be the wrong solution.