I am rebuilding my 258. Is a non stock camshaft worth getting if the rest of the engine is stock? If it is worth the extra $$, what cam should I get?

It is always worth the $$$. The stock ones are always tame so at least go for a small step up so whatever mods you may make work all that much better. What is really worth the time is doing a light port and polish aand match the gaskets. This will add very noticable horse power and with the cam it will be even better.

What is a good cam for a stock motor? The only mod done to the engine is a MC2100 and no computer. What spec's should I look for (lift,duration,etc)?

OK what would you pick.

.05 Duration Lift Lobe Centers
I / E

1 208/208 420/420 110/114
2 208/208 432/432 ????? - Clifford
3 206/214 462/485 111/111
4 204/216 456/484 107/117

It's all your preferance. What do you want? Low rpm torque? High rpm horsepower? Are you rock crawling, or running mud pits? Clifford makes 4 or 5 different cams & they list the best power range & characteristics of each. You should be able to figure out what you want from that info.

I am looking for good torque/low rpm for off road and in town driving, verry little highway. All of the ones I have listed state that they are for low rpm torque. I was wondering what the difference between them would be? Would it be noticable? If so, how?

I don't know that much, but here's an idea:
There is probably at least one person in Pheonix that grinds custom cams & would explain evey detail. I know one person who did this & it was no more cost than buying a cam off the shelf.

For me I don't really give a crap about all the torque since a 5hp motor will get the rig down the trail just fine due to all the gear reduction. What I am looking foe is something that is more in the 10000-5500 range so a 206-210 cam is the ticket IMHO. I run a V6