Your comparison is not really accurate. Nokia are helping to produce a community/reference UX that will not include integration into OVI services (maps, chat, mail, etc...). Google have released Android 2.3 with *all* features and Google service integrations intact. People complain about not having voice navigation in Maemo, but the Meego Reference UX won't even have maps to begin with. Upgrading your N900 will not give you an equivalent experience to what you currently get from Maemo.
Regarding phone upgrades, I always buy phones free of contract yet I only upgrade phones every couple of years. I will not be buying the first Meego device simply because I only bought the N900 12 months ago. Next december I'll be looking around again, so that will give me time to evaluate whether Nokia do start supporting Meego *and* upgrades on the same device, or whether any of the Android manufacturers and doing better in this regard. If I were buying today it would be Android, but who knows what the situation will be a year from now.