Thanks for all the feedback. Glad to have it confirmed I've got enough space (and therefore no reason to pussy out!)
Sawhorses sounds ideal for spotting, can't believe I didn't think of that - and they're certainly cheaper than buying spotter rails or building some blocks. I'm a rank beginner so I won't be needing blocks for a good while yet (if ever) so I'm happy to leave them for now!
Michael, I wish I had space for both a platform and the power rack, but sadly it's one or the other. The garage is the only space I have to train; I'm not likely to move house anytime soon; and there's nowhere for it outside (plus it rains here more days than not). All things considered I think the platform gives me a lot more options than the power rack, mainly because it lets me go overhead. Plus all that space will mean I can actually do pushups and other metcon stuff without contorting round the rack's uprights. I'll be sad to see the rack go, it's done me proud in the past and it feels almost wrong to sell such a good piece of gear, but life's all about these little compromises I guess.