I think the object of lavish is what is being given, not the one to whom it is given.
So I may lavish gifts on my friends, but I may not lavish my friends with gifts.
I don't know if this is personal or general, but it means that I cannot lavish myself.
I can, however, spoil myself or indulge myself.
I think you are technically correct, but after years of reading advertising, I see that people are often exhorted to
lavish yourself -- so I think I've succumbed to ad-speak.
And with that admission, I'm going to go lavish praise on myself -- effusive, extravagant, perhaps even fulsome, praise.