Brakes/Shifters on older bike
I have a 1994 trek 850 Mountain Track, 21 speed. It's still in good condition and I've put tons of miles on it over the years, used to be my only transporation in college. Recently, over the last year or so it has sat and not been used much. The brakes need adjusted and the shifters are not functioning properly. I'm planning on replacing all the cables for the brakes and gears, since I'm sure they need it. They are stock from when I bought the bike.
My questions are:
Is it worth redoing the cables? The brakes are shimano cantilevers, should I just upgrade to v-brakes? If I upgrade to V-brakes, I need to upgrade the levers as well to work with v-brakes, correct?
If I upgrade to v-brakes I'll have to upgrade the shifter as well, since my current is shifter/brake integrated, correct?
And if I upgrade the shifter, do i have to worry about finding a derailleur that is compatible with the shifters, or are they pretty much standard?
Any info would be appreciated, thanks Alot!