David I have been giving your situation some thought. If I were starting out with limited budgets I would be investing in a total VST situation. The reason is that there for a start are a heap of free VST's. One great one being Superwave P8 for example. Light on CPU use, very powerful, looks a little like a Roland analog synth and can sound like it too. So much music can be created now from just virtual instruments alone and free ones at that. Then invest in one or two paid ones like Alchemy or UHE or Zebra etc.. There are so many great new VST's being released all the time.
And classic synths like Moog or Oberheim etc are being so well recreated in software it is not worth having the machines themselves. I had them all and they are creating all sorts of maintenance problems these days. They are not worth what they are going for today either. They have just attracted some sort of stigma. A lot of 90's instruments are very difficult to get parts for and some parts are failing now from that era. Don't waste $4000 on an Oberheim when the VST sounds incredible for like $59. I have owned an OBXa and know the sound of it very well. This plugin is amazing and sounds exactly like it, I am pretty flawed as to how good it is. This shakes the floor just like mine did. All 12 oscillators on one note opening up. This is just an example.
http://www.sonicprojects.ch/obx/welcome.html Music first, then performance then tools etc..
If you do save up some money I would invest in something like a late 90's workstation that you might score for $500 or less. Something like a Kurzweil K2000 maybe optioned up with some extra memory and sounds etc.
(better still is the PC3 if your budget can go higher) Still way powerful and can do a lot. Learn to drive it and you will get years of enjoyment and you can produce endless amounts of music. A synth like this can be multi timbral and still sound amazing doing 16 parts at once all with its own effects too. It lightens the load from your computer and also acts as a controller talking to your computer inputting your playing into your VST's
Other options might be a Roland Fantom or Korg workstation of some kind. Then maybe invest in a small analog synth if you wanted to be able to play with knobs fiddling with the sound while it plays etc.. You can set up modern controllers to control VST's too and so much expression can go in that way too. You might pick up a bargain at some store as well. The synth should be something a little higher than a home keyboard type thing too if you can manage it. Just some ideas.