Upgrade or replace early 2008 Mac Pro? I have an early 2008 Mac Pro that I use for research involving a lot of statistical computing. Some of this requires a decent amount of memory (storing hundreds of thousands of iterations of simulations, each having many parameter values…). It's fairly slow and seems to be swapping a ton on many of these runs. 

My question is how easy and how cheap would it be to add memory and maybe a SSD to speed it up (I don't care about processing speed on its own that much). I don't want to invest a ton of money in a machine that might soon be obsolete (e.g. not supported by new OS versions), but I don't have a ton of money to blow on a completely new machine.

What about other options for a new Mac? Would a new iMac with lots of memory be comparable in cost to the total upgrade price for my current machine? I'm not super tech savvy so don't have a good sense for whether throwing many hundreds of dollars into a 7 year old computer is dumb. Advice would be greatly appreciated.
Based on personal experience, the 08 Mac Pro is well worth squeezing that last bit of life out of.

It will take 64GB RAM, as 8 x 16 - even though Apple say it will only take 8GB sticks. Best source, other than OWC [which I think is US only] is eBay. There are specialists who sell old Mac parts &amp; RAM; &amp; mostly list with specific models items will run on. DDR2 is not cheap, though. I think I paid 300 quid for 16GB last year.

It's possible to add an SSD in one of the optical bays - without losing any existing drives in the main bays.
You will need a 2.5" > 5.25" mounting bracket, a PATA > SATA power cable &amp; an SATA data cable [straight ends] maybe 9" long [don't get the shortest one, it won't reach]
The power you get from the optical bay itself.
The SATA connection comes from 2 'hidden' extra connectors - on the motherboard, behind the main fan assembly, which you can route behind the optical bay as you refit it.

Clone your existing boot drive with something like Carbon Copy Cloner &amp; away you go.

The speed increase from the SSD alone is astonishing.