Thanks for all this information.
I did discover the metrorail info on the Museum district website sometime yesterday. Seems like there's a *lot* to see in the Museum district. Also - the Museum district is very close to a lot of highly rated restaurants. So we can - for example - go to lunch at Underbelly and then go to the Menil. Using the metrorail - our feet - and perhaps a cab or two. We only have 3 full days - and spending 2 in the Museum district doesn't seem out of line considering what's there.
In terms of transport to/from the airport - I'll check with the hotel and find out what its limo rates look like (for $25/more or so - a limo is worth it - for $100 - it isn't).
I assume late April is pretty late for "spring flower season" (we're directly east of Houston and it's too late here). But - if I'm wrong and there are any gardens you can recommend - let me know. Robyn