Yes wait until the haswell refresh and then upgrade to the nMP. if you have an 8-core now the 12-core should be within your price range with the nMP.
I have really started to notice the strain while trying to edit 1080p/60 videos and 4K timelapses in Final Cut Pro X and editing RAW stills in Lightroom 5 on my Early 2008 Mac Pro.
I feel like I've souped this 8-core 2.8GHz girl up about as much as she'll go: SSD, 18GB RAM, RAID, Radeon 5770 1GB, etc.
My problem is that I'm not sure what to replace it with. A casual review of the benchmark charts here (http://browser.primatelabs.com/mac-benchmarks) seems to indicate that even the current (non-Haswell) Retina Macbook Pro outperforms my rig now.
Do you think that one of the upcoming Haswell rMBP would be sufficient for editing 4K timelapses, 1080/60 video, etc. or should I step up to the upcoming Mac Pro Trash Can edition? I already have a 30" display so the notion of getting the high end iMac doesn't interest me very much.
...or should I get both?