I wouldn't plan on too many nights in Dallas. Its a fun town but there are better places to visit in Texas. If you do decide to stop here, be sure to spend some time in the Fort Worth half of the metroplex too. Sometimes we get overlooked but there are some interesting things to see and the two cities are very different.

But I would strongly recommend that you drive the extra distance to see San Antonio instead. Its only an hour south of Austin. Of course Austin is fun too, so you will want to see some of the sights there as well.