Protocol, nothing more.
Remember, Clinton gave a fine eulogic performance at Nixon's funeral. It's just part of the duties of office.
I was at the dedication of 41's library....I fully expected W to attend - I think it's to accept the Library on behalf of the American people. Also expect to see 41, Peanut, Pres Ford (if able); and at 41's, Nancy Reagan spoke (it was a great speech), and I believe one of the Johnson girls (I think Lady Bird had just had her stroke), Caroline Kennedy, Nixon's daughters (or at least one)all attended... well, you get my drift. It's courtesy and custom. BTW, the dedication ceremony was one of those kind of days you never forget. I was extremely lucky to get an invitation and got to see Gov W speak and he introduced Jeb as governor (which told the crowd that he was running for Gov of FL again). What a wonderful day it was!
And...I hope the lovely Laura accompanies our President. The two of them will be the stars of the day and will outshine the rest.