Hi James,
There is a B&B regularly advertised in Birding World that offers "almost guaranteed" Pine Martens; though it's not in Speyside unfortunately ! It is at Lochcarron ( Tel 01520 722377 ) I haven't tried it yet, though hope to next Spring, so would be interested if you do get there....
With regard to the hide at Speyside Wildlife, we tried it last year for £ 18 for the evening ! Total failure on the Pine Marten front though a bunch of Badgers and Wood Mice did their best to entertain us - more worryingly I know of at least 5 other nights during last Spring/Summer when other friends failed as well, so unless things have changed for the better, or you've got deeper pockets than me, it might pay to locate them at a B & B !!
All the best,
Steve.