Autodesk no longer support GMax but it is still available for download. I've played with various modelling apps over the years including Maya and Lightwave, overall for what you get with 3DS MAX I've yet to see anything better but then it all gets down to personal preference and what you know/ have learned/ feel most comfortable with.
BTW I use the 'Scale' feature in Max to alter dimensions, scale over either x,y or z axis or combo's thereof.
Glad to hear that GMax is still going, that one was a great idea IMO.
Don't get me wrong, I love 3DS and still actively use it. SolidWorks is in a completely different field. Maya and Lightwave are competing products, SolidWorks is not in competition with 3DS. I actually use both in conjunction with each other. Engineering models are designed in SolidWorks and then imported into 3DS for texture/animation. I modelled my cabinet in SolidWorks and imported to 3DS for painting, graphic designs etc.
[pimp]
If you scaled the width of your cabinet, your side panels would reduce in thickness. Trust me, if you can ever get your hands on SolidWorks give it a shot. Sounds like you've got your experience in 3D modelling and that will carry through to SolidWorks easy enough.
I was going to stop my pimping there but I'll leave you one little tid-bit. You've no doubt had your share of pain with boolean operations in 3DS
In SolidWorks you don't even think twice about drilling holes in the CP. I have a pattern sketched out mapping hole center's that can easily be changed in either mm or inches. Routing has been done where joysticks will be mounted and I have even cut out the t-mold groove. Overkill? Yes. But try boolean that in 3DS... and then change the width of the panel
[/pimp]
okay, yes it would be possible to adjust the width of the CP even after all the Boolean operations if you left your Modifier List in tact.