I have both. I really like both. I did put a complete 590 front end on my 500 though because I dislike the 500 screw on barrel design. I don't like the polished stainless bolt on the 500, but I plan on taking the whole thing down and doing a camo job on it.
The 590A1 is a hell of a gun. It's just a rugged beast. The heavy walled barrel does add quite a lot of weight. I would recommend just going with the 590 special purpose. It's a good compromise. Unless you're running a huge amount of rounds through the gun in a short time, you don't need that huge thickness.
Anyways, yes, I think the 590 is worth the extra cost over the 500. The A1 has the cool factor of being a military shotgun, but whether those changes are worth it to you is something you have to decide for yourself. I'd definitely recommend the 590 style though.
Glock 19 G4 BFG | Glock 17 G4 FDE | S&W M&P 22 | Ruger GP100 4" | Sig P226 MK25 | Sig P320C 9mm | HK USP 9 | HK USP 45 (Tan) | HK P2000 9mm | HK P30L 9mm | HK VP9 | Walther PPQ 9
Daniel Defense DDM4 V4 | Arsenal SGL 21 | ASA Side-Charger SBR | Savage Mark II FV-SR
Mossberg 590A1 20" SP | Mossberg 500 Cruiser