No such thing as too many PS references. That's where most of the development of the planes came from anyways, it's hard to avoid referencing Planescape almost like how it's hard to avoid thinking of Paris when you think of large cities in France, only more so.
However, whereas Planescape treated the planes with depth and concern for large scale conflicts between law and chaos and good and evil, belief versus substance, etc, the Planar Handbook doesn't go back to that. Instead, it treats the planes as gigantic dungeons in another dimension to go kill things in.
For instance, the Planar Touchstone sites, all 32 pages worth. Most of the space is not the descriptions of the places themselves, but the encounter and monsters you have to defeat at each place to gain the listed powers from that site.
For instance, there's one in Sigil that you go to and defeat or otherwise avoid the monsters that you roll up on the random encounter table given for the site. This 'establishes' your PCs in the area and gives you less chance of an encounter when you visit the site. This is patently stupid. It's in the middle of a freaking city, what the heck is this all about 'establishing' yourself at the site by beating the monsters you meet there. No, it's likely to gain you being marched in front of the city courts for a trial is what it's likely to do.
Each one of the sites is similar in that respect. You go there, you beat up the monsters that inhabit the site and gain a power. You visit it in the next year to recharge the power and potentially fight more monsters. It's like a freaking respawn site in a hack and slash MUD.
Most of the sites are really cool, but the coolness ends there. The way it's all implimented is an excercise in idiocy. It's insulting to roleplay and insulting to any campaign that exists outside of the shallows of a monster killin' dungeon crawl. Go visit the planes and meet strange and exciting people so you can kill them and take their stuff is what it seems to push.