First of all, you are misusing a few common terms, so let me clarify them.
Each monster in that book has a Challenge Rating (CR) that, when compared to party level, translates directly into an XP award. A Challenge Rating is a measure of how easy or difficult a monster or trap is to overcome. (Dungeon Master's Guide, page 36)
The Party Level is the average level of all characters in the party, including player characters and npcs.
The effective character level (ECL) of a creature determines how powerful it is as a character or a cohort. The Monster Manual contains statistics and other details on potential cohorts. Take the level adjustment plus the Hit Dice (including class hit dice) to generate ECL.
A little more about adventurers and economy
Remember that unless something is a trade good, like gems, pieces of art, magic items it is sold by half of it's market price. Keep in mind, that player character are adventurers. They need to purchase and sustain some sort of transport. They must eat, drink and have a place to sleep. The spellcasters may need to purchase expensive material components, like the diamond used in resurrection spell, that must cost at least 10 000 gp. There are other factors as well, like hiring npcs, paying a spellcaster to cast a spell on them and purchasing one-time use goods like potions, scrolls. Whenever I play as either Game Master or a Player, the wealth is quite fastly used is some way.
The question itself
The wealth should never be used when determining the character or party level, however it could affect the gained rewards, if you find that encounters were considerably easier because of the wealth.
Modifying XP Awards and Encounter Levels
Sometimes, the circumstances give the characters’ opponents a distinct advantage. Other times, the PCs have an advantage. Adjust the XP award and the EL depending on how greatly circumstances change the encounter’s difficulty. (Dungeon Master's Guide, page 39)
There is also a small table, that suggests how you should modify Encounter Level and the awarded XP.
| Circumstance | XP Award Adjustment |EL Adjustment |
| Half as difficult | XP × 1/2 | EL –2 |
|Significantly less difficult| XP x 2/3 | EL –1 |
|Significantly more difficult| XP × 1-1/2 | EL +1 |
|Significantly more difficult| XP × 2 | EL+2 |
It is suggested to keep the further points in mind while modifying XP reward and ELs.
- Experience points drive the game. Don’t be too stingy or too generous.
- Most encounters do not need modifying. Don’t waste a lot of time worrying about the minutiae. Don’t worry about modifying
encounters until after you have played the game a while.
- Bad rolls or poor choices on the PCs’ part should not modify ELs or XP awards. If the encounter is difficult because the
players were unlucky or careless, they don’t get more experience.
- Just because the PCs are worn down from prior encounters does not mean that later (more difficult) encounters should
gain higher awards. Judge the difficulty of an encounter on its