A common situation.

Is it generally worth it for Black to swap the R + P, giving up his N and B?  That's equivalent points (5+1 for 3+3), and weakens White's castled king.  But in exchange, Black has given up two mobile pieces to take out a single immobile Rook.

Thoughts?

Nope, the two pieces are generally much better. A more equal trade is a minor piece, a pawn, and a positional advantage for a rook. The numbers are relative, and not applicable here.

Check out the "Dilworth Variation"; the Russians infused new life into it to bolster Black`s chances.

Generally the two pieces coordinate better than the rook and pawn. Even in the endgame where the mobility of both sides is greatly increased. In the specific situation you posted I don't think any strong player would even consider it.

Think of it this way, if you were in the endgame and the position was as follows:

White

2Rooks

5 pawns (3 on the kingside, 2 on the queenside)

Black

R + B + N

5pawns (3 on the kingside, 2 on the queenside)

In general most players would agree that the exchange you are suggesting would negate Black's material advantage.  N + B will outmanouver a lone R in almost all positions.

Only under exceptional circumstances where tactics would make possible, the queening of a Black pawn impossible to stop, or an unstoppable mating net, or an exchange to set up a draw through a perpetual check or stalemate if you are about to be mated or if White is about to queen a pawn by force in order to force a 3 move repetition or perpetual check or a stalemate.