Is there a Mitzvah to be Oleh Regel in today's days (meaning when there is no Beis Hamikdash)?
I have a little pamphlet of t'shuvos/analyses by Rav Mirsky that basically concludes that there is, especially fulfillable by feasting and dancing. I will try to locate, quote, and cite it.
Update: See Sha'arei T'shuva 529:4 (last one in volume 5) and the sources he cites for related information.
If I recall correctly, the basic obligation is not there, but many consider it a meritorious act to make it to Jerusalem or the Kotel for the holidays anyhow.
(I think he was quoting Tzitz Eliezer and -- yibadel l'chaim -- R' Ovadya Yosef).