Those problems don't mean it needs a rebuild. Oil leaks could be bad gaskets, look what happened when you replaced the oil pan gasket. Sometimes vavlve covers can get twisted a little if they are tightened up too much, pull it off and see if its still flat maybe. Try a little sealer on the gasket. If your carb is crapping out fuel, then it is definitely not right (unless it just was flooded). Thats probably why its not running well. I would definitely rebuild or replace your carb before doing the engine.
If you really think the engine is worn out, do a compression test on it. If its worn, it'll show in the results. But from what you said, I suspect its a couple of much less complicated and expensive components and maybe adjustments giving you trouble, that defintiely the place to start.
