A lot of people go on about "Tier 1" classes or full caster classes "breaking the game" or "overshadowing" the others - this is not entirely correct.

The truth is that they can do this, if played that way, but usually don't (unless everyone optimizes hard). They play to be effective and have fun. One of the most effective ways to play a wizard can be as a party buffer. Yes they really effect the power balance of party v. monsters, but overshadow fellow PCs? - they do the exact opposite by making them so much more effective.
Most potentially game-breaking spells are 9th level (yes not all) and many campaigns never reach them, or if they do they are not abused. Breaking a game is rarely a player's aim - they are there to have fun too and breaking a game kills that.
So looking at lower level tricks, a lot of them seem to be very situational (which means prepared casters do not use them as they need to prepare a flexible spell load) or not very repeatable - which means no one uses them as no one wants to stop for the night directly after breakfast when the sorceror says "yes I just single-handedly killed all the enemy guards, but now I need to regain my spell slots" - too high a chance those guards will have been replaced.
[Caveat: if you managed to get a party to bounce (i.e. run away) then the chances are that the prepared casters will come back with spell lists tuned for that fight - this tends to make them short.]

In short one only needs to deal with the potential power imbalance if it becomes a problem, otherwise you create the problem!
A lot of people play fairly average pure casters, e.g. clerics that mainly heal but carry some fun stuff to chuck around as well (after all if the cleric does the fighting, who does the in-combat healing?). These characters can be quite easily overshadowed by an optimised fighter other "low-tier" character. Apply flat penalties to pure casters and you just make things worse!
your method will make the fighter reach 11th level before the wizard and cleric reach 7th. This means that either they get killed in one hit by a critter that is a fair opponent for him, or all the monsters die in one hit from the fighter.
Also D&D is balanced for a high magic environment - healing, long term buffs, combat buffs etc. - if you make pure casters cost twice the xp then a lot of player swill not (and rightly so) touch them - and the game will then go straight out of balance (no serious healing for a start).

The best option is usually to run with the rules pretty much as they are, but warn players that if they find tricks to abuse you will take issue with that. If they do stuff that you consider "rules abuse" then discuss it with them and see if they can help you come up with a fix.
If someone dominates the party too heavily, again discuss it (with everyone) and see if anyone has good suggestions on how to resolve it.

A lot of people forget that most RPGs have age ratings on the side that are actually quite high - they are there for a reason, gamers are expected to be reasonably mature. In that light try behaving as if we are all mature - people might surprise you.