the resolven thing would be a full on show rather than a meet, yes sarn services would be a great starting point for a run, the problem you got at this time of year is most people take their cars off the road until show season starts which is usually around march time.
we did a run a few months back with my club (Blue Oval Enthusiasts Club) for our south wales members, we headed up through the rhondda valleys to brecon then abergavenny, raglan and back on the m4 and home, it was a great day out with a couple of photoshoots and some grub thrown in along the way.