In general, it's best to keep topics focused in one thread which is why crossposting is "against the rules"/discouraged. In the future you can always ask a MOD to move your existing topic to a thread you find if you feel it would get more attention. But in the end no harm no foul.

You are a little late but not too late to the game. For myself I'd honestly suggest doing DEN-LHR and DUB-DEN for experience & availability. Then doing London to SNN/DUB as a cheap cash ticket or train & ferry ride. London is a great city and the combination of London + Ireland makes for a good trip. Availability into London can usually be better with the variety of options for airlines & routings. If you were to do London on the return you'd incur the ADP tax for premium passengers but not for transit or arriving passengers.

BA also is a UR transfer partner for the short hop between the UK & Ireland if you wanted to also do that as a redemption but be sure to checkout actual fares first & be aware of the taxes on redemption tickets as they may be about or even more than the fares available as BA, EI & FR fly those routes. As BA or IB Avios can be a good value & useable also on EI you may find that favorable for award inventory and/or fees involved. With both UA & Avios programs you can do 1-way awards so search both for inventory. Avoiding AA&BA for the transatlantic will save you quite a bit compared to other programs. If flying EI back to DEN I'd look for flights via ORD, LAX or SFO over BOS or EWR. Also look into ET's DUB-LAX flight as an option. In the Spring I believe UA had seasonal nonstop to London also or one can connect via MUC, FRA or other gateways giving you a solid J experience and minimizing domestic/intraEurope premium classes which aren't much to scream about.