Now is the time to buy. MacPro just got refreshed so you can get the latest and greatest if you want to spend the bucks. If you hold on to a system for a while (sounds like you do) it makes more sense to get the most up-to-date system when you make the move. The new systems should be shipping in a few weeks.
But if you want to save you can often find new but last gen models at a discount since newer normally brings faster for the same selling point as the old models.
Money spent on getting a system setup correctly is always money well spent.