There are few characters who wouldn't get
some benefit from an extra few caster levels. The thing to consider, however, is the opportunity cost.
For instance, for both rogues, it competes with Stealthy and Nimble Fingers. In combat situations, it also competes with improved initiative, weapon finesse, weapon focus, two weapon fighting, improved buckler defense, dodge, mobility, spring attack, and elusive target. It also competes with the various social feats for the social-skill based rogue as well as things like Disguise Spell. (The ability to work a charm person into what appears to be ordinary conversation could be more important than the extra duration on a heroism or invisibility spell). And, it competes with the combat options too. Even social rogues get into fights every now and then.
Depending upon the class makeup of the rogue in question, the benefits might not be too significant either. If the majority of the character is in rogue levels with only 4-6 caster levels total, then the difference between a 40 square foot door (about 6x6 feet) and a 100 square foot door (10x10) may or may not be sufficient to be worth a feat for the rogue/wizard. The lower number is big enough for enlarged doors and some double doors anyway. The higher number still isn't big enough for castle gates. So, the benefit consists of being usable on doors somewhere between double sized house entryways and castle gates. Since sneaking generally isn't done through the front door anyway, it's a relatively minor benefit.
Similarly with a glibness type spell (Glibness is bard only so it doesn't properly belong here, but heroism offers skill bonusses that might be valuable), the difference between 50 minutes and 90 minutes (as a 3rd level spell, there's a minimum caster level) is significant. However, 50 minutes is often enough to get in and out and finish. 90 minutes is sometimes not enough. A lesser metamagic rod of extend spell can solve some of the duration problem making the un-feated spell last 100 minutes and the feated one 180 minutes. Still, it's a limited number of situations where 180 minutes is good but 100 minutes is not. And there are other ways around most of those situations.
Both of those characters have to ask themselves not "would an extra 2-4 caster levels be useful?" but rather "is the ability to affect 10x10 doors instead of 6x6 doors or 180 min extended heroism rather than 100 minute extended heroism going to be more helpful in avoiding trouble than Improved Initiative, Iron Will, Weapon Finesse, or Elusive Target would be in helping me survive trouble?" The answer won't always be yes.
Practiced Spellcaster is a good feat for a character who wants to do something useful with one or two levels in a casting class. It's also good for a character who wants to use ordinary spells in combat but lost a lot of caster levels for some reason. Mystic Theurges and Arcane Tricksters will often fall into this category. For a character with middling spell skill (like a roge with 4 or 6 levels or wizard), it doesn't make as much sense. Their caster level is already high enough to do most of what they want to do and the feat won't push it high enough for them to function like a real caster. For spellcasting characters whose combat contribution is not straightforward spellcasting (like my eldritch knight character), it's not a particularly good feat either. Their caster level is already good enough to do most of what they want in combat and it isn't caster level that keeps them from effectively using attack spells anyway.
Malimar said:
Practiced Spellcaster would allow your Knock spell to affect ever larger doors (10 square feet per caster level) from an ever safter distance (100 feet + 10 feet per level) and you would be able to stay invisible for longer (1 minute per caster level). Other infiltration spells that would benefit from higher caster level: disguise self (duration), silent image (area effect), ventriloquism (range), rope trick (duration), etc.
And that's just 1st level spells. Practiced spellcaster looks pretty tempting even with infiltration emphasized.
Glibness lasts 10 minutes per caster level. 10 minutes can get you past the guards. 60 minutes can get you past the guards, the doorman, the maid, and talkative butler, and straight to the fair maiden.
And other witty spells that greatly improve with caster level: disguise self, silent image, charm person (duration), eagle's splendor (duration)...
The feat still sounds pretty good in that scenario too.