Thanks so much for your replies.
I spent a wonderful 10 days in Vienna. I took a train to Bratislava for the day and arrived in time to take a walking tour around the center. I found it somewhat disappointing that there are few residents living there, and most buildings are now occupied by banks and embassies, but it was nice enough. I went off on my own afterward, and had lovely time walking outside of the center. I found a lovely park, did some photography and took an early evening bus back to Vienna.
I also did the trip to Melk, with a trip down the Danube to Durnstein and Krems. I hoped off at Durnstein, but wanted more time on the river, so got back on when the boat returned from Krems, took it upstream to Spitz, and then back to Krems, giving me a lovely three and one-half ride. It was perfect.
I loved Vienna, so much that I extended my six night stay to 10, and hope to return in the future. Lovely, vibrant, beautiful city.