This series has some good episodes but many so so ones.
One of the biggest problems, especially after Season 3--the sons don't really have consistent friends. Sudsy and Hank both exited. Tim had already exited by the end of Season 2. Other than Ernie (who became a brother) and some short lived or rarely seen people--the sons have no consistent friends (Gordon for Ernie is a short lived exception).
Further, beginning in Season 10--Chip and Ernie barely appear in many episodes and especially in the case of Chip don't appear at all. The show lost its My Three Sons feel (even though Katie, Barbara, Polly, and Dodie are great additions imo--its just that the three sons aren't really much of the show season 10 and after).
In this episode specifically--Chip and Ernie don't appear except in a clip from an old episode. Robbie visits Bryant Park and who is he going to visit? After Hank, he doesn't have a friend from there that we really know of. Robbie's "old friends" in this episode are ones did not appear before. Who is the groom? Generic guy we don't know.
It all adds up to a lifeless episode--with pictures of their old house being the only actually touching moments and that kind of epitomizes the series as a whole as it continued and finally crashed bad in season 12 when Robbie left, Chip appears in maybe 1/3 of the episodes, and Fred MacMurray doubled as his Scottish cousin or whatever.