I would do it, Rivera is getting up there in age although he will have a good, but not great year. Nathan is a stud, Halladay(if healthy) is a stud, and you'll be getting the best catcher in the draft...Abreau is overvalued this year imo.
If you really need starting pitching help, then it's a pretty good deal.
Martinez is a huge upgrade over AJ, while Nathan is only a slight downgrade from Rivera. You're definitely getting a great part of the deal in Martinez/Nathan for AJ/Rivera.
Halladay is probably 15-20 picks below Abreu in a draft, but that's not a bad deal as I see it.