Quite...if you've got a OM21/2.0 (which exists, as does the 3.5) I'll pay 300 for it, no probs
Market price is more like 450 for the 4.5 and over 500-600 for the 2.0.
Landscape doesn't require crazy fast glass - you tend to stop down, shoot from a tripod, all that fun stuff. Also depends on how you want to shoot your landscapes - not everyone likes ultra wide (I don't on full frame most of the time), and my most used landscape lenses are my 24-105 and Contax/Zeiss 35/2.8. Sometimes the 17-40L. Most of my favorite landscape shots are stitched panos, the single shots are often 'longer' than 24mm. Depends on you style - 'landscape photography' is NOT synonymous with 'ultra wide angle' (which I consider anything under 24mm FF equivalent to be).
You can't really go far wrong with the 17-40L. Great glass, fits both cameras, decent range on both, good to very good stopped down, and you won't see the corners (weakest spot) on 1.6 or 1.3x crop. It's just not very wide on a 1.6 crop..