word choice - "Don't you think?" vs "don't you think so"?

Life would be a lot less painful without love, don't you think?

Life would be a lot less painful without love, don't you think so?

To some extent this might be a matter of opinion. However I'll give mine.

1. I would say that:

(a) 'don't you think?' is almost a throwaway line that seeks (and probably assumes) confirmation of the speaker's opinion.

(b) 'don't you think so?' is a request for information. It seeks the opinion of the listener.

2. I would expect a difference in intonation.

(c) 'don't you think?' would be unemphasised and take a descending tone.

(d) 'don't you think so?' would be stressed on the word 'think' and would have a rising tone towards 'think' followed by a descending tone afterwards.

Note

Intonation and stress are very important in such cases. The way you speak a tag question can change its effect quite strongly.