For older CPUs (pre-A6), not really. The old CPUs were pretty much just barely good enough to run the mobile OSes at release and a major firmware upgrade with some performance penalty. Beyond that and you get significant slowdown.
Right...but buying now, the Air2 or the Pro 9.7 are the only contenders.
If the Air2 came as a 256gb model (which of course, they don't)...with a $75-100 off sale, bringing the price down below $500...I'd be very tempted to buy then. That would set me up to comfortably wait till for an OLED iPad years later.
I'm pretty sure I'm going to get the Pro 12.9 v2, but if the Pro 10.5" debuts before that happens and depending on how it's spec'd, I may look at that instead.