C’mon, you can’t dismiss 26″ and still be considering 27.5″. You’re an intellgent man, you know there’s bugger all difference between them.
If there really is a perceivable difference between them then, when you say “something perky that loves manuals & wheelies etc & loves just playing”, that screams BMX to me, ie. smaller wheels = good. Plenty of tall people manage to ride BMX’s so you know the height thing is bull.
Re. obsolescence. Go to your local trail centre and you’ll see that at least 80% of the bikes being ridden are 26″. Only things to worry about regarding obsolescence are frames that won’t take a tapered fork IMHO. Even if all 26″ forks ceased production tomorrow you’d still be able to stick a 27.5″ fork on and never notice the difference.
I’m reasonable tall (6″2″) and when I wanted a bike for mucking around in the woods I went with a Slackline and couldn’t be happier with it. If you want to go 27.5″ then there’s the Switchback.
I don’t know why I wrote all that as you should buy whatever makes you happy, but your (and plenty of other peoples) reasoning for dismissing 26″ always seems slightly misguided to me.