no current plans to fly internationally in the near future I don't really see a reason not to use them.
So, use them for the RDU-SEA business seat. The points are worth less than nothing if you never use them (I say "less than" because you could have spent your time/effort earning some other points that might have actually used). Points value is always subjective.
As for the question of valuing points by the cost of a comparable revenue J ticket: many people (and I'm among them) don't value points based on the retail cost of the seat I'm getting, but rather on what I would have got if I had to pay myself.
So for a domestic trip, I would have bought the cheapest Y (economy) seat and I use that number to value the points. Your RDU-SEA trip looks like $600+ right now, so your 50k points J (business) award seat gets you at least $0.012/point, which doesn't seem like a horrible value, plus you get at least a slightly nicer travel experience.
However, the same flights (US Airways connecting through CLT, just as an example) would cost $1250+ in "first" class. That would seem to value your 50k points at 2.5 c/point, which is a great value. Thing is, no way in hell I would pay $1250 for that flight nor burn 50k points for it. Those "first" class seats are 37" seat pitch (only 6" more than economy) on small- to medium-size narrowbody planes. Those are the old style "business" seats you think of when you think of a domestic flight. So I would not use the "First class" ticket price to value those points, though perhaps value them slightly higher than the $0.012/point I mentioned above.
For comparison, I recently flew business class to the middle east through Europe and Asia on several long-haul flights on several airlines. Each flight had around 70" pitch fully-flat or nearly-flat seats, widebody aircraft, excellent meal catering, extensive drink selection, good lounges pre-departure. Most flights were less than half full in J even thought Y was sold out. I usually had a pair of full-flat seats to myself, enough floor area for at least 6 economy seats. The basic trip could have been done for about $1k, and I burned 150k points, so my actual cash savings would suggest a value of about $0.006/point - horrible. A business class flight would have been $4k+, suggesting I got a really good (but perhaps not exceptional) value of $0.027/point. In reality, I would never have paid $4k for the business seat, but the travel experience was immensely better than economy, so the "value" is somewhere in between the two. On top of that my routing was complicated and would have actually cost even more to do on a paid ticket (whether Y or J) than a simple round-trip to my final destination. So, my value for points is even better than the math would suggest, but there is no practical way to put a number on it since booking that as a revenue ticket would have required calling a travel agent or airline and getting them to manually price it out (I had to call to book it on points too, but they don't bother to calculate what the price would be, only if its allowed within the rewards flight rules). Maximizing your stopovers and other routing flexibility on awards tickets is another way to get more for your points, but it's hard to quantify the value.
I personally prefer to save my points for intercontinental J-class travel, but I do have plans to fly internationally (and expect to continue to have such plans until I'm physically no longer able to travel). If you don't, then use them for the travel you do have planned.