Sanding with a scroll saw does not do a good job it just works. It does not sand square and you still have fuzzies to deal with. The fuzzies are smaller but they are still there. I can't imagine how a jigsaw would better at sanding.
If you sanding a lot of inside cuts in your scroll work you are doing something wrong. Wrong blade, dull bale, cutting too fast for the blade you are using, and bad wood. In good quality hardwoods and even better grades of softwoods, you can get mirror-smooth cuts.
With modern quality scroll saws moving the blade to another hole is very fast. About ten seconds. This video is why I bought an Excalibur EX-21. This is very important if you are doing a production run or cutting portraits that may have hundreds of inside cuts.
https://youtu.be/bUC7wutR3A4
No jigsaw for me. I'll keep that money for a new Pegas or Seyco scroll saw.