Just to follow up on this... As noted above, we stayed at this place --
http://terrace-motor-inn.com/ -- which was, indeed, right on a lake, and had canoes, pedalboats, etc. to check out. However, we ran out of time and didn't get a chance to use them.
We drove on a Tuesday afternoon, had dinner in town, then went back to the hotel and crashed. We got up Wed. morning and basically did the HOF all day -- arrived around 9:45 (enough time to let any right-when-it-opens lines to die down) and just happened into a 10 a.m. guided tour of the plaques, which was a cool way to start. When that was done (30 min or so), we checked out the plaques some more, then headed to the museum.
We did an hour or two of the museum, left for lunch for an hour or so, then came back and did probably 2-3 more hours of the museum -- as much as our little ones could take. (I probably could have spent a little more time looking closely at each display, but we did get through the entire museum.) Not a ton of Astros stuff on display, as you might guess (and most of what was out was Nolan Ryan stuff). I think my wife took photos of just about every Astros-related thing we saw.
Aside from the obvious big stuff, my favorite single item on display was Pudge's Astros jersey from the night he broke the MLB record for games caught -- which just so happened to be a few hours after my son was born (we watched that game in the hospital that night). I got a photo of him with that display, which was fun for me.
After the HOF, we had dinner in town (New York Pizzeria, which I highly recommend), then walked around town a bit checking out shops and such. Went back to the hotel that night and left in the morning for the next leg of our trip. I think we easily could have spent another day or two there, either returning to the HOF (me), enjoying the lake (the rest of the family), or checking out a few other things in the area (the Farmers Museum looked interesting). Overall, a good trip; thanks to everyone here for the tips!