I think the key issues are really whether you have the interest/motivation, and whether you want to swap year groups to be honest.
Also, find out what intercalating in each of the areas will entail. Do yoiu know anything about the project supervisors?
I know my intercalation was different as it was compulsory, and I had little choice in what I did, however, mine was a rather lonely 9/12 as basically stuck at home or the library with a forests worth of research papers, questionnaires, and databases. It was however a good experience in terms of research, as it's becoming increasingly important to do this as an SHO/Reg.
If you're very motivated, it could be a good experience. My time of intercalating was less hard core than the rest of medschool has/will be, and I enjoyed being able to organise my own time, and get to do things I wouldn't have otherwise done.
I think ethics&law would be a realy valuable BSc... wish I'd have had that option!