After my May trip I'm glad I didn't go to Moher. I'm just disappointed I went to Dingle. Northern Ireland seemed to be exactly what I expected, so that was good. I made the mistake of covering a few must sees in the Republic that I'd missed on my first trip. They were mostly disappointing because the ratio of tourists to locals seemed to be 20 to one (or more). Who knows what it's like in summer months?
Even in May Dingle was 100 percent tourist trap. Slea head drive is mostly non-sights that charge admission and are open exactly the hours the tour buses operate. I'm glad I saw the Oratories. A good rule on Dingle peninsula, if it has visiting hours, skip it. Actual historical sights can be visited early. I paid 2 euro for one ring fort (drop in a slot), nothing at either of the Oratories or the 12th Century Norman church. Other than that, time on Dingle was a complete waste. If you dropped in at the sights suggested in RS Ireland book, you'd spend 30 to 40 euros in admissions for generally cheesy re-creations - not including what you spend on snacks they sell.
Ring of Kerry has better views and better, less touristed, sights. The traffic on Kerry is primarily people making the ring drive and staying in Kinsale or Killarney which gives Kerry a much quieter feel, outside the daily traffic jam, compared to Dingle. I found I could completely avoid traffic on Kerry pretty easily. Especially out on the end where buses don't go.
I enjoyed the Cliffs of Kerry - even though I was hoping for sunset views and found out they aren't always open. When I did visit, there were a very small number of people (less than ten) in a very large area. I'm not sure I'd say they're better than Moher but they're higher and certainly spectacular.
I enjoyed our overnight on Inish More. I can see how that's becoming too much of an attraction. Not only do you have to pay to visit Dun Aengus, for example, but your photos are polluted with "Don't Climb" signage. As a rule there I'd suggest, the further you walk to see a sight on Inish More, the better chance you will have it to yourself. Going outside the ferry hours also reduced crowds considerably. Unfortunately admission hours for Dun Aengus limits the ability to visit outside of ferry hours. If you can, try the other ring fort. There is also a ring fort up near Derry, Grianon of Aileach, that is worth a visit. There was some signage about open hours there but no locked gates. We had it to ourselves in the morning.
If I planned my trip today, I'd skip Dingle, Moher, Galway and focus more on the northwest. I'd also take any town people suggest seeing off your list and visit only small towns no one has heard of. For my trip the best lodging and best meal was at Roundstone, it was not tourist-free but not nearly overrun.
Biggest disappointment was the lack of traditional sessions. Sure you can see professional musicians seven nights a week playing traditional songs (just like in Temple Bar in Dublin) but there is a completely different feel to local amateurs coming together playing for a local audience for the love of music. The best trad session I saw was a Sunday night in Dublin, that's somewhat damning with faint praise.