Really, it's all just personal preference (and perhaps "what you're in the mood for at that moment").
But for me, a singer is sort of like a guitarist. If a singer is simply wailing at the top of his lungs (and range) for the whole song, to me it's sort of like listening to Ynwgie Malmsteen (or any other speed-metalish guitarist) play a million notes-a-second for 5 minutes. Impressive at first, but it quickly gets BORING. High-end range for a singer is AMAZING when it's saved for the "punch" of the song.
A prime example (for me) is Enchant's "What To Say"(the song's about a guy dying from brain cancer, and what he'd say to his 6-year-old son if he could still speak...based on true story, BTW). Although Ted has a high voice, anyway, when he hits that really high chorus of "I hope that you won't forget me," it STILL sends chills down my spine. If he'd sung the entire song at that altitude, it would have completely lost its punch.
Another example: Listen to "Used" by Pain of Salvation, and you'll hear Daniel using a fair chunk of his considerable range to perfect effect (and that's the key word: EFFECT), building and building until it hits its emotional, lyrical, and vocally-high peak.
That's one of the reasons why I was less-than-blown-away by Stratovarius (truth: I fell asleep. Really.). While their singer has a great voice and awesome high-end range, and the guitarist is very talented (and they were both dead-on in concert), after the first couple of songs, the NOVELTY of the singer's range and the guitarist's speed wore off, and I was left...well, asleep.
Some people just don't like high-pitched and/or falsetto voice, but for me it's all about HOW it's used, as well as how often...just like speed for a guitarist/keyboardist, or other instrumentalist.
Chris Salinas' brilliant performances in both Power of Omen's "Test of Wills" and Zero Hour's "Face The Fear" are also stand-out examples of HOW to use incredible range to incredible effect, IMHO. He's one of the top singers in metal today, as far as I'm concerned.
But again, it's really all just personal pref.
Craig