If you are using US DM or UA MP miles, you should not have any problem routing via Europe instead of TPAC, as long as you stay within the MPM/routing limitations. I'm not sure if JFK-FRA-SIN-xxx would be too far out of the way, maybe someone better with KVS than I can help out here.

As far as booking on SQ with any *A award, SQ does not release C or F seats on the A380, 777-300ER or A340-500 for Star Alliance awards, so the only long-haul C or F *A award seats on SQ are on the 747-400 (now limited to SIN-FRA-JFK) and a few secondary destinations (mostly in Europe, like ATH and CPH) that still are getting the 777-200. These aircraft that are available for *A C awards generally do not have a full flat bed, at best, you will be in the SpaceBed (inclined-flat bed). My recent experience was BKK-SIN on one of these older aircraft (still working on the TR), the cabin was dated, but well maintained and the service was outstanding. Any routing via SIN is a bit out of the way for you, but a short to medium layover at SIN is actually quite nice (the airport itself is quite nice and the SQ C lounges at SIN are some of the nicer C lounges out there), and a longer (20-23 hour) layover at SIN gives you some time in town, which is easy and quick to get to from the airport.

I think if you ask a dozen FTers whether NH or OZ C is better, you get 3 votes for OZ, 3 votes for NH and 6 votes for "about the same." Both have a new staggered C seat that has been deployed on some flights, and an older recliner C seat on most flights. Both have very good cabin service in long-haul.

AC, UA and CO all have widely deployed full-flat beds on long-haul, with different advantages and disadvantages to each. Cabin service isn't as good as the asian airlines.