The way I understand the question is how to make a dex based mounted charger, and the following is my solution attempt.
Hey I Can Chan mentioned a great solution (using a magic item to make a lance a light weapon), but it depends on the GM being okay with it because the lance is only a one handed weapon while mounted.
If he is okay with it here's how to get the most out of it:
- Weapon Finesse (duh! it's why you got that lance-upgrade) for Dex to Attacks
- Spirited Charge for x3 damage on a mounted charge with a lance
- Agile magical property (on the "light" lance) for Dex to Damage
- Piranha Strike for slight Attack penalty for increased Damage
However, even if he says no, you're not screwed yet, if all you want is a dex based charger.
You can still get double damage while mounted charging with Spirited Charge using other weapons.
If you have Str 13 you can take regular Power Attack with a agile Elven Curve Blade (and Weapon Finesse) for decent damage. - You'd want Power Attack over Piranha strike, because it let's you increase the Damage bonus you get when using two handed weapons (which the Elven Curve Blade is. It being light means you can "finesse" it as well). Note that it's an exotic weapon proficiency (thus requiring special training/feat) unless you're an elf, for whom they're martial.
Alternatively if you don't have Str 13 and you can't afford agile a Dervish Dancer (Dex to Damage if Scimitar and off-hand empty/not used) with Weapon Finesse and Piranha Strike gives you double damage with Dex to Attack and Damage while doing a mounted charge while wielding a Scimitar as long as there's nothing in your other hand.
However it doesn't match the fluff of Dervish Dancer very well (given that you're not going to be dancing on the horse you're on...)
If neither of the above get any agile light weapon with Spirited Charge, Weapon Finesse and Piranha Strike.
Perhaps a rogue with the Scout archetype (sneak attack when charging at level 4) could add some damage potential.
Lastly as a Paladin using Smite you'd get extra Damage (in certain circumstances, a lot in some campaigns) -- which combined with a lance charge can lead to some surprising damage.