Nigel - I did not. I'm on ST 3.5 but in view of the complaints I read here, e.g. cclarry, who tried 3.6 and lost settings, I have not upgraded. ST 3.6 appears primarily focused on pushing their new custom shop.
I'm going to make my own instruments with FX and engine settings matching what's in ST 3 for similar instruments and see how that comes out. My concern about Miroslav was that it was going to take a lot of experimentation based on being unsupported, and so I'll have to figure out pretty quickly if it's worth it, or if I should switch to a more modern set of samples. I'm looking at EWQL HO and possibly some Kontakt package should NI decide to page all their new symphonic stuff in a package at a reasonable price. I'm still writing, so I don't need to make final decision for a few months.
I have no concern about the $35 I paid for MP, only the time it will take to get it working well.