[RPG] Two handed damage on a lance while mounted

No.

RAW, no, weapons do not break themselves. Only damage explicitly done to objects via sundering or striking an object apply. The rules in Damaging Objects are the sum of how you can do it; if it's not there it's not there for a reason. They also don't say your weapons don't disintegrate every Tuesday, "it doesn't say it doesn't happen" is not a logical argument about a ruleset.

Furthermore, lances aren't more fragile than any other two handed wooden hafted weapon in Pathfinder. (Nor were they fragile in real life - jousting lances were specially hollowed but ones for real fighting were as sturdy as anything else.)

You can house rule that damage applies to weapons - but given the inflated damage numbers of Pathfinder, weapons will be breaking on every hit. Over level 3 hits routinely do 15+ points of damage per strike and that would explode a lance or spear or halberd every time. So then you'd need to do "half damage" or something and it becomes a logistical challenge. Note that weapons become "broken" at half hit points and provide a penalty and are completely destroyed at 0 hp. If implementing a weapon damage rule, I'd take it to a more realistic level; maybe do 1d6 damage to it on a natural 1 (or maybe a number equivalent to the hardness of the thing being struck).

You and @KRyan are correct.

• all multipliers work alike (crit, lance, brace, whatever);
• everything is included in the multiplier except bonus dice
• multipliers are additive not multiplicative, see Multiplying Damage, Core Rulebook 179

It doesn't say anything more about it because there's nothing more to say, the rule is simple and all-encompassing.

Your math is slightly off however. For a tenth level paladin with STR 22, Spirited Charge (req: Mounted Combat, Ride-By Attack), Power Attack...

• BAB +10
• Lance: 1d8 damage
• Magic enhancement: +2 to hit/+2 to damage
• Strength: +6 to hit/+9 to damage assuming you're two-handing the lance
• Power Attack: -3 to hit/+9 to damage
• Base Melee Attack: +15 to hit, 1d8+20 damage
• Charging: +2 to hit (-2 to AC)
• Smite: +10 damage vs evil, +20 vs "super-evil"
• Mounted and Spirited Charging: +17 to hit, 3d8+60 damage
• Smiting Too: 3d8+90 damage vs evil, 3d8+120 vs super-evil
• On Crit: 5d8+100 vs normal, 5d8+150 vs evil, 5d8+200 vs super-evil
• The aristocrats.

On a crit, you can one-shot a Hezrou (CR 11). It'll live through the first non-crit shot, but you can get it with the next normal blow (assuming you make your save against the blasphemy...). Yes, that's how it's supposed to work. Yes, it's pretty hardcore. You can only do it 4x/day and need to set up a mounted charge and to crit, though. But many super-optimized builds are built around charging for this reason.