Roll casting is definitely a challenging skill to master. Honestly, I've never found a huge use for it. When you're on a stream fishing for trout, I think that it's better to let your fly drift away from the target and then recast, rather than trying to fix what was probably a bad cast by roll casting. If you're on a lake/pond, then just pick up your fly and recast. Most lake/pond fish aren't spooky enough that you need to worry about false casting over them.
There are a couple of exceptions where I will use a roll cast. First of all, if I'm in a position where backcasting is difficult. The second case is if I'm in a position where I want to get the fly under some overhanging brush that a normal cast would land on, rather than go under.
Most of all, roll casting takes practice. If you're able to do a 35' roll cast with a 3 wt, then I think you're doing pretty good. I wouldn't worry about it!