Whom ever installed the wet vent, if it was done correctly, was a pretty good plumber I imagine. Wet vents are tricky and the code language is confusing to some. But for those who can figure it out, it provides a drainage system that uses less pipe and less fittings and therefore has less chance of leaking. Are you having problems with any of the fixtures? The system you have is as efficient as you can get and should work great. The added bonus of wet venting a lav, shower and toilet into one stack is that it provides an extra "scrubbing" in the pipes and helps keep them clean. The only time you'd ever maybe have an issue is if someone is taking a shower and running the lav and flushing the toilet at the same time. I'd stick to what you have instead of trying to change.