If you're going to carry much on the back you should probably move to some sort of cassette hub since they put less stress on the axle. Around here, decent mtb wheelsets go really cheap, keep your eyes open and you're bound to find something sooner or later.
Personally, I'd stick to 7 speeds or less, especially if you want to go indexed. For touring or just tooling around you don't need that many gears and the tolerances for 7 speed are much more forgiving than 9 or 10 speed. A 7 spd mtb wheelset will often be spaced to 130mm so you won't have to spread the rear end as far either. It is also a lot cheaper to get 7 speed parts than 9 or 10 speed.
If you're on a tight budget I'd just ride it the way it is for a while and upgrade as needed. New cables/housing, chain, brake pads, tires and a thorough cleanup and lube can make a huge difference in ride quality without busting the bank. If you do decide later that you want to upgrade certain aspects then go for up but you might be surprised at how much you like the bike just the way it is before then.