Plumlee is a much better passer. he is a comparable rebounder (very similar TRB% though Thompson is better). Plumlee scores at a much higher percentage from 0-3' and shoots a much higher percentage of shots from 0-3' so he is a more efficient scorer, though has even less range than Thompson. Plumlee blocks shots and generates steals at a much higher rater, but also turns it over at a much higher rate. Plumlee has better WS and WS/48, a better BPM, a better VORP, etc.
In other words, I actually think Plumlee is slightly better than Thompson and he makes less, though has the extra year. I don't think either does a whole lot to the actual wins and losses. In a vacuum I'd swap Thompson for Plumlee and wouldn't give it much thought, but I wouldn't want to add any real value to the trade to get it done. I like Ellington as well, but again not worth a 1st to get done. If they wanted to do Plumlee and Ellington for Thompson, Green, cash (to cut Green or whomever), and BOS 21 2nd, I'd do that. Would throw in the 22 2nd as well if I had to. No 1st's and no young players (of any real value) though because there is no point in giving up real assets for such a nominal gain.