interested in a mod that gives xp when destroying towers

I haven't heard of one.

It should be straight forward to do yourself. Though as I haven't done it myself, this is only what I think will work.

The defense structure folders you are looking for are here.

\dgdata\units\ug\b

Open up the relevant folder for a specific structure and you'll see the unit.bp files.
eg: UGBDefense01_unit.bp

Since towers do not grant XP, You'll need to add a section like

Experience = {
        Radius = 30,
        Value = 20,
    },

and fill in whatever values you think are appropriate

There is of course more work than this to build a mod... but the other steps are the basics like creating and filling in the mod_info.lua file etc... covered in other posts.

Yup - there's not one that I'm aware of.  If you are looking to just mix things up with rook,  I trust you'd at least be entertained a bit by this mod:

http://forums.demigodthegame.com/399792

Don't modify your game files directly, that will not let you play in multiplayer with anyone else and may break the game completely if you do something wrong.

Here's a mod that adds XP and gold for tower kills:
300 for archer towers
500 for ToLs
1000 for forts

http://code.google.com/p/nubletsupreme/downloads/detail?name=TowerRewards.zip

Extract directly into your mods folder.

for you miryaka - hopefully the op checks out this thread and sees what you wrote for him.