A party or celebration is never a bad thing, and a first anniversary is always a good reason for either! If nothing else, I look at myself in the mirror and say "well done, girl!" and be thankful to have had another year of life.
My first was special, I felt, because you are definitely over the hurdle, back to "normal" life (whatever that is!) and the tests are all looking good . . . . it was almost like getting home from hospital, in a way. It meant that I could put it into the back of my mind, I was somehow no longer a "heart patient" but the valve had just become one more part of my medical history, it was no longer omething I had to think of on a constant basis. I know, that probably sounds like trivializng the whole thing, but it was rather the opposite; kind-of like the honeymoon is over, now let's get on with this marriage thing . . . hard to put into words, maybe someone will be along who is good with words and will do it for me!
Anyway, congrats on the big O-N-E !