Euphoria --
There are several reasons why it might be showing up more. First of all, on a weight basis, 4-mar is more potent, so that could make it cheaper to make. Second, it is not so easy to get ephedrine or pseudoephedrine in the quantities needed to make a decent amount of meth. It is even HARDER to get good quantities of the other reagents.
Now, PPA, which is the precursor for 4-mar (with the CNBr synth), is not exactly easy to get either, but is overall far less watched by the DEA than ephedrine/pseudo. However I do not think people are making it via the CNBr route. Cyanogen bromide is somewhat expensive and very difficult to obtain. It must be handled carefully, although it isn't quite as much of a bitch as some may claim. And there are other reagents that can be used and that are easier to get. Now, using CNBr you get a mixture of 4-MAR isomers that is very potent (trans), whereas with the other reagents you get a weaker product. The street stuff I have had matches up well with my theory that people are NOT using CNBr, as the stuff is on the weak side and does not feel like trans-4-mar.