Just my two cents.
For what it is worth, I would like to add a thought to the discussion.
It seems the feats as proposed would limit the increased caster or manifester levels to such spell variables as duration and damage. I believe the primary motivation for this limitation is to make sure the psion or other manifestors do not receive bonus power points from the feat.
If this is the concern, then I would propose that the feat explicitly disallows bonus power points, but allows the character to have the higher caster or manifester levels for other purposes.
I am thinking specificly of the prequisites for item creation feats. Often the caster level requirements for the item creation feats are higher than are required for the creation of specific items. The result is that, especially in a lower level campaign like LEW, a multiclass caster or manifester is unlikely to be able to take these feats.
As a side note, The table and the text of the SRD disagree. The table states that bonus power points is dependent on class level, while the text gives a formula for bonus power points that is dependent on manifester level. If we simply accept the table over the text, then perhaps we could do without any restrictions to the feats. Basicly the feats would read as the following:
Practiced Caster/Manifester
Prereq: Ability to cast 1st level spell / manifest 1st level powers.
Benefit: Choose one of your spellcasting/manifesting classes. Your caster/manifester level with that class is now +4. Your caster/manifester level may not exceed your hit dice. This increased caster level never result in addition spells/power points per day nor additional spells/powers known.
Special: This feat may be taken more than once. Its effects do not stack. Each time you select this feat apply its effects to a different spellcasting/manifesting class.