I don't think being fast or slow has any bearing on whether you use power, as long as you're committed to improvement. I'm fast-ish enough to podium local XC races/team 24 events etc./ride with the fast local chain gang, but I'm not genuinely fast - compared to 'proper' riders I'm rubbish. And I'm a slow ITT'er in comparison to many (I need sleep!).
But despite not being talented I use power to train on the road (powertap on my winter bike, stages on the summer bike, no power on the mtbs). I find it really useful and fun. I'm a scientist so love the data, you can measure improvement (it doesn't matter whether you're fast or slow, getting stronger is fun), and target weaknesses/identify strengths, and manage your training load. Training to power makes turbo training manageable (and with two young kids and a busy job getting outside is sometimes not possible). I enjoy training and trying to get the most out of myself physically.
That said, since the HT I've been riding purely for fun, doing steep stuff and jumps, and haven't done a decent set of intervals for ages
I'd be interested in having a power meter on the mtb - but not sure I could use it to train to as power is often dictated by the terrain. As for using one in an ITT, I think it would be valuable if you knew how to use it in relation to your own physiology, and your major goal was the competition. I'm never going to be competitive, so while I like to turn up to events in decent shape, once I'm there I ride on feel (no HR monitor, no power, no speed/av speed on the GPS, just time of day and distance) and enjoy the experience.
Back to the chaingang tonight though!
