Visiting a city the 2nd time is a good way to enjoy a city. I was in Sofia at least 7 years ago for a salsa festival and I had some nice memories. Sofia is a very small city and architecturely not as eye-pleasing as cities like Vienna or Budapest. It is famous for their vegetables, yoghurt and rose oil !
We went to this expensive and highly related restaurant with a Serbian chef. It was good but salty and towards the end we could barely finish our food. Strangely, all 3 of us had stomach problems so we suspect its their food.
I was lucky to attend a salsa event (lv10) that is hosted in Hotel Bulgaria on Friday. It was ok . On Saturday we went to a Milonga in Hill Hotel (lv6)which was quite dismal in my opinion. Both tango and salsa scenes are relatively small.