RE: How useful is a playpen/playyard?
Our PNP has 3 main purposes: 1) downstairs changing table; 2) travel bed; and 3) toy bin. I find it indispensible as a changing table because it keeps me from going up and down the stairs at every diaper change, but that doesn't appear to be an issue for you. I do use the PNP when we go on trips, mostly to visit relatives. You do need someplace for DS to sleep when on trips. Unless you always stay in a hotel and request a crib or can easily borrow something, you'll need something that you can tote along. I seldom used the PNP as a place for DS actually to play. He doesn't like to be confined, so that didn't work. However, that depends on the disposition of your child. My nephew is content to play in the PNP for extended periods.
If you get one, the Grace Pack 'n Plays are nice and fold up fairly easily. At this point, you can probably go with a basic one as you really don't need a bassinet or changing table feature.
Mommy to Justin (13 years) & Ashlyn (8 years)