I have! Removing the soundpost ( or rather sound-slab, 'cos it's a hefty 1" thick piece of hard maple) has two dramatic effects:
-the acoustic sound immediately opens up, and becomes more a conventional ''jazz guitar'' sound, and less electric-sounding
-the guitar starts to feed back like any other 17" guitar - as you'd expect.
I think I agree with the advice to trade in, rather than attempt removal - and I say this having done it! These slabs of maple are just not designed for easy removal, and I was lucky to have been able to do it at all.
How I came to remove the soundpost is pretty simple - I have had a 50's x500 for some time, and love it. I have been looking around for a westerly x500 recently, and by luck a couple came up in the London shops. I missed one by a couple of hours, and went to see the second one, ready to look hard and bargain. This blonde guitar was overpriced, I got the price down substantially, looked hard at the neck angle, frets, action, and pots, played it through the obligatory shop fender amp set to ''chainsaw'', and bought it. What I didn't do was look inside the f holes!!! It was only when I got it home and was setting it up that - yes, I know!! - I noticed that inch-thick maple slab inside.
With the slab, the feedback resistance is excellent, and the tone is very good indeed through an amp - so it would suit everyone except a jazz player who needs to practice acoustically, and who needs that particular jazz hollow-body sound.
Anyway, having just bought it, x500's being pretty rare around here, and not being able to face the thought of a long wait and a hefty trade-in loss to fix the problem, I decided to cut through the soundpost. I think I have a reasonably balanced, not purist, view about guitar modification, this was a 90s model not a 60s model, and after all guitars are instruments made to be played, not antiques to be put in a glass case. Anyway, cutting through involves tying back the pickup wires up through the f-holes to avoid cutting through them , removing the back pickup, and VERY carefully sawing through the post in two places, near the back and under the bridge, through the back pickup hole while protecting the finish. This involves sawing at a very tricky angle, and particularly avoiding digging into the back while making the lower cut. It was one of those jobs that makes you sweat while you're doing it and that, when you have finished it, you KNOW you are never going to voluntarily do again. I still have to removed the remnants of the block on the guitar back, which I'll do by steaming it.
Just thought I'd share this, in case anyone's interested. To repeat, I only did it because I didn't expect a soundpost on an x500 and simply didn't look out for it when buying, and I bought it for jazz playing only. And, with the soundpost in, it's certainly a more versatile and still fine-sounding guitar; those laminated spruce tops are superior to any maple-ply tops, as on 175s, or carved-tops for amplified playing. But, without a soundpost, the sound just improves enough to make it worthwhile, at least for me. If I need to sell it, it will be a lot easier to re-instate the post than it was to take it out.
Am I glad I did it? yes....would I recommend it to others? well, I think anyone reading this will guess the answer to that...
Oh, and about the point about the top being strong enough - even without the ''post'', the braces are quite substantial, and the bridge break angle is fairly shallow, so no risk of the top sinking that I can see. The top on mine hasn't shifted since the 'surgery' at all, and that's with heavy strings.
Chris