Hi @delishtreats! There are many activities being held on a daily basis in many parks, especially in this one. The palace is huge offering many halls to be used for art works and culture events.
I haven't been night time there, but I am 100% sure the fountains, the palace and some other sites are being lightened up at night time.
Gorky park, or Park Kultury (nowadays) is I guess in top 3 Moscow parks, it is big by size and conveniently located by the river, but of course Moscow is huge and to explore it you need more than a few days :)
btw. Where are you from?