Welcome to FT, Mojos_Pride!

I noticed no one has jumped in here, so I'll give you my two cents. Others may have more sage advice...

Obviously it is a given you want to go as far out of the way with your connections as you can to maximize miles. Connecting in SFO, FLL, MCO or LAS are good ways to do that for DEN-EWR. You probably know about the MileCalc tool to do this math for you.

One additional thing you can do is add a second connection each way. Often you can do this for little to no extra money. You'll end up with DEN-(non UA Hub)-(UA Hub)-EWR and vice versa. You might find an itinerary like: DEN-LAS-IAH-EWR and EWR-FLL-ORD-DEN for the same price as DEN-XXX-EWR-YYY-DEN. Even an extra short connection (like EWR-BOS) will give you a minimum 500 miles additional. I know you like to avoid ORD, but because of its central-hub location ORD will show up in a lot of these searches.

I usually use matrix.itasoftware.com to play around if I'm trying to maximize miles. Type "c:ua+" in the advance routing code (multiple UA-only flights) and be sure to select "Up To 2 Stops". If you do this with a round-trip search, it will likely only give you 2 stops in one direction and one stop in the other. Try doing two one-way searches to find a 2-stop itinerary each way.