These questins are always tough. We dot know how much you enjoy resistance or how much you woud like some variety.
I can tell you that the expansion seems to be compatible with avalon.
True. Our group rather enjoys Avalon. I didn't bother getting The Resistance since we first played Avalon and love the characters one can play with. A different theme is all well and good. I still think I would introduce people with Avalon though. It seems to be easier to learn when the concepts are from that perspective.
I am leaning towards doing it since there are some things that I don't have - like the Avalon promos and of course the new stuff they are throwing in. The 14$ base is also not bad.