So I've got a (as I'm sure you can tell) 2005 Kona Lana'i. I got it new, in 2005 for like 350 dollars (I think). I didn't do much with it (light commuting.. waste I know), but this year I have started to go out on trails, I think I've taken about 10 rides on the thing. The brakes suck (I had to replace the rear brake cable as it was actually pulling the housing out of the brake lever cause of the friction...), but I think I might be able to tune them up more.

To get to the point, I'd like a better/more responsive/more braking/less breaking (the pedal broke on the first ride ) bike. I'm sure you all understand.
Is it worth it to try to upgrade this frame? I'm not sure if it is drilled for disc brakes (are they just tabs on the left side of the rear triangle?) and if it isnt, could I do a v-brake in rear/ disc in front? Could I/would it be worth it to get a new fork/ disc brake(s?)/ wheelset and then maybe transfer those to a better frame some time?
Really what I'm asking, should I bother with upgrading this or should I just save up for a whole new (and better) bike? I really enjoy mountain biking and would like to get as much out of it as I can.
Thanks all!