What I tend to use and believe in is creativity and imagination. If you can build something that nobody has ever seen or done before, plus use different paint schemes, decals, scratchbuilding methods, diorama scenes, etc., then I feel you'll have a fighting chance of competing at a contest.
If you've ever read any of my posts, you'll know that you have a kindred spirit in me regarding that philosophy, CB... I've typed (endlessly, to some) many a word about the art of Scratch-building, Imagineering, and Creative Gizmology and their place in this high-dollar, AM-Parts over-populated hobby... That "12.00 on Ebay" 1/32 Revell Mustang III is as likely to win gold as the 120.00 Tamiya Mustang if the Revell modeler's got his "poop in a group"...
That said, and I've judged at a LOT of shows (primarily dioramas) over the years, I'm a firm believer in the premise that after-market parts simply are a "lazy" way to super-detail a kit, and the best stuff comes from the imagination and skills of the builder, not the AM Parts rack... They're fine if one feels that they're necessary to have included in the kit, and that's what the builder enjoys doing (I have no earthly idea why one would spend even more money on what is already likely a ridiculously high-priced kit anyway), but when it gets to the point of replacing 50-75 % of the kit's interior "greeblies", you're likely suffering from AMS and it's probably terminal...
One of the judging criteria used is "Scope of Effort"... A scratch-built seat/harness assembly and throttle quadrant, along with some wound-wire oxygen hose and stretched sprue hydraulic line that cost the builder about 15 cents in materials is going to garner more points from me in effort than a 25.00 P/E version of the same (provided it's well-done)... Also, the stuff doesn't need to be bolt-for-bolt accurate... Suggestion is a greater (and easier) asset than duplication... Especially when it comes to items that would, for the most part, be unseen without the use of a right-angle fiber-optic flashlight (although, I HAVE one, lol)...
No amount of after-market parts will save your model from being passed-over for recognition from me faster than one loaded-out with a hundred dollars-worth of PE and resin parts, but with big ol' fingerprint on a windscreen, an unsanded mold-parting line on a tire, or, horror-of-horrors, a diorama depicting a truck or aircraft on the grass, but NO tracks... (You'd best be explaining to me, somehow, where the helicopter that dropped them in place is)
Many modelers (especially the younger ones, in the 18-29 group) have gotten so far into the AM world that their skill-sets have stagnated at the point that if it can't be bought and added, it can't be done... And part of the blame for this can be dropped on judges who're easily "blinded by the brass", since they themselves probably fell into the same trap early on in their "serious modeler" years...
I've even read the words, "Contest-Quality Model", in here... That's a lot of bunk.. Practically EVERY model (there are few exceptions, but they ARE exceptions) is "contest-quality" if one learns the basics, practices them, expands their techniques and modeling-material "list", always pays attention to the details, AND the judges are experienced (both as modelers and judges), knowledgeable, and well-informed as to what the judging criteria is and (more importantly), ISN'T...