As usual, what you want to do with the gear is going to dictate which road will be best in the long run. But not as much as the sound it makes and what it inspires you to do with it. That being a rather noncommittal answer, I offer my experience as a real-world solution.
I've held onto every synth I've ever purchased, starting with a MicroMoog in 1976, followed by a Yamaha DX-5 in the early 80s, an Ensoniq EPS in the mid-80s, a used Chroma Polaris in the early 90s, and most lately a Kurzweil K-2000 just after they came out. Only the Kurzweil and the EPS are seeing any action in my home studio these days-- the Kurzweil because it has the best sounds overall, and the EPS because while the samples sound a little dated (when I bother to load them off floppy), it's still a great controller.
The EPS comes in handy because I'm finding myself moving more and more toward software-based solutions, that is, soft synths. I'm OK with the MIDI recording, and I can get a decent feel for tempo, but when I actually commit the audio of a Kurzweil track to disk, I'm pretty much stuck with that sound at that tempo till the end of the project. And if I decide that after the rest of the tracking, the Kurzweil timbre needs to be a bit brighter, or the piece needs to be a bpm or so faster or slower, I need to record the part
again after making the proper tweaks. Having everything in software gives me a lot more flexibility for making production decisions on the fly before I finally commit to a two-track mix or master.
At this rate, I can see a day in the future when all I'll have in the studio room is an
M-Audio Keystation Pro 88, my PC, my desk, and a halfway decent LDC.
That is another factor you'll need to consider as you weigh the binary versus the brick-and-mortar-- the cost of a PC and a decent audio card (hint: it won't say "Creative", "Sound Blaster", or "Audigy" on it) and the time you'll spend tweaking it to get the best recording performance. I find it's worth my while building my own PC and configuring it, and I was able to do the PC for $600 (I had the $700 Layla for my audio interface), but that particular adventure is not for everyone.