To make treasures/relics/whatever more prone to generating interactions, they need to be made way more visible on the strategic map...
Right now (I play KenWood since I'm on Debian Stable) the only thing easily seen on the strategic map is animals (bright pink) and trees (green), and secondarily stone (grey) and thirdly metal (yellow, but not bright enough to be easily distinguished on the map, depending on what surrounds it).
Even berries are quite difficult to spot (slightly different green) !
There at least should be a map mode that shows only resources, and probably a way to toggle which resources to show (so it could be possible to show only berries, or only metal, or only treasures, or only relics,...) making very easy to spot whatever the player is interested in.
And relics are not visible outside the vision range of a unit, which means that if you send cavalry to scout the map, you need to micromanage them in permanence (checking if there is a relic in their area of vision).
I never played multiplayer (I'm too old to play on faster than "slow" and I don't think anyone is interested in playing at this speed) but on single player I found treasures stressful (if you don't get enough of them you lose) and tedious (it's not only a matter of exploring the map quickly but to be lucky enough to notice them which means spending not only cavalry but also constant player's attention).
And they never lead to any interesting cavalry combat (either I get first to them, the enemy gets first to them, or I get to them too close to the enemy so that his infantry chases my cavalry : the later case may need some micro skill but usually no real tactic involved since I have very little chance to defeat them as my cavalry is stretched thin in order to find the other treasures).
Maybe make treasures either more numerous and smaller or needing more force to capture ?
On some maps they're defended by Gaia soldiers but I'm not a fan of it especially when the treasures/gaia forces are too close to the starting point.
Maybe have the treasures/defending-forces under a non-capturable building (but not impossible to destroy without siege engines) that sounds an alarm horn (audible/visible by all players) when attacked ? That would leave the option for all players to go try to get them or to attack enemy cavalry/citizens/women (if women get a "dismantle" ability) trying to get them...
Or make the treasures visible to everyone at the start of the game ? Especially if they're defended (so that it's not the closest player that gets them, but the most committed), that would allow for real strategic interaction early game...
Is it technically possible to have treasures be carried by the unit that fetched them ? Or to have one trader unit at start (trainable in Civic Centers but with a very long time, like 60 seconds, so it's not unremplaceable but still not a good idea to have it killed nor possible to spam them) which would be the only unit able to fetch the treasure ? That way ambushing the units carrying the treasure would be a possible strategy.
Actually, the One-Trader-at-Start option would make collecting treasures a real strategic endeavour, and not a lucky grab (to get more than one treasure the player would need to defend the others while s/he manages his travelling salesman), so if it's technically possible it's probably the best option...
(and no, I don't know how to make a mod)