Not all Asian countries even have visa exempt entry.
For example for me (Oz) I need a visa to enter Vietnam and all that's available is single entry tourist visa 30 days. (Not cheap)
When things are made easy and flexible (as they are in Thailand) some folk still complain.
You mention travel and sight seeing.
From Bangkok jump on plane to Udon Thani and stay few nights. Chill bar area.
Quick easy drive from UT to Nong Khai for your 45 day gift that has extention available.