Will be traveling to Amsterdam from London. We have 3-1/2 hours at Midi Brussels. Is this enough time to see anything outside the train station? Thanks for any help!

If you can get rid of your luggage, I would suggest to take the train to Brussel Centraal (Bruxelles Central). It's only one stop, 3 min. - trains leave every 5 min. or so.
You will be right in the city centre then. Walk to Grote Markt (Grand Place) and the surrounding streets. Have one or more beers on a sunny terrace!

What is the best way to get rid of luggage? Do the train stations still have those locker storage areas?

francophilie03, I looked it up for you.
Yes, there are lockers in Brussel Zuid (Bruxelles Midi).
Small locker: 1.98 eur/24h
Medium locker: 2.73 eur/24h
Large locker: 3.22 eur/24h

The Grand Place is a practical goal and definitely worth visiting. Just remember that you have to go through security to get on the Eurostar - so allow enough time to catch your train.

smueller,
Since DAB will be traveling FROM London, she won't have to go thru security anymore and can hop right onto the train to A'dam.

This forum is such a helpful tool--many thanks!