Spending XP, an alternative to leveling up in D&D.

There are some Role-playing games out there that have a different stance on how to level up. As I have lately been playing Final Fantasy 13 and Dungeon Lords I have been looking at a way to incorporate their levelling system into D&D.

How the levelling system works in those two games is you gain experience points (or crystal points in Final Fantasy 13). You can then spend these points into levelling up your attributes (such as strength or magic) and learning new skills and abilities (such as learning new spells). This is different to the normal levelling system in dungeons and dragons where you gain feats and abilities upon reaching a certain amount of points. You don't spend the experience points, it just represents how much your character has learnt across encounters.

However, this method feels unrealistic as we learn and apply abilities as we encounter them. We don't become better lock pickers by watching people over a few weeks and then trying it out our self and instantly becoming better at it. It's all about trial and error. We learn better by watching first then trying it out our self.

I prefer levelling up by spending experience points because you don't have to wait a long time for an exciting spell or waiting to upgrade your attributes. So, I thought, why not try and incorporate it into Dungeons and Dragons?

To be honest, I struggled. I do have the 4th edition books but I don't know a lot about 4th edition yet and how the levelling system works. So I blew away the dust on my 3.5 D&D books and reminded myself of the levelling system. I decided that the abilities you should be able to level up using this method would be skills, abilities and feats. I left out health points, base attack bonus and base saving throws because I felt it would complicate things even further.
I looked up how much experience a level 20 character would acquire over their development and it would be 190,000. Now assigning how much experience should go into each domain (ability, feats and skills). The most experience should be assigned to the ability area, less in feats and the area with the least amount of experience should be skills. Therefore:

190,000 experience all together
Abilities - 80,000
Feats 60,000
Skills - 50,000

For everyone rank increase in ability, feats and skills, you increase the amount of experience points you need to spend to increase it. This is to ensure that you don't get 5 ability points spent within the first 5 levels and therefore over powering. I wanted to make sure that every 4 levels you gain 1 ability point and 1 feat and spend all your skill points.

Regards to skills, this is a difficult area to figure out as different classes have different amounts of skill points to spend. Also, intelligence influences how many points you can spend as well in skills. Therefore, I think one way to figure it out is to assume firstly that one skill point will be spent per level. Once that is worked out, you should divide it by the skill points available. For example, a rogue has 8 skill points to spend per level, if they have +1 intelligence modifier then they have 9 skill points. Lets say we worked out it costs 200 experience points per rank to increase a skill up by one rank. For example, to increase it to the 5th rank you would need to spend 1,000 experience points. However, as the rogue has 9 points to spend per level, it would cost around 110 experience points. You can see how messy this is but I know something can be sorted out!

To be honest, math isn't my strong point so any mathematicians out there who is good at creating formulas then get in touch below and contribute! Any other comments are very welcome as well!