One of your big problems to me would appear to be less a matter of lack of RP opportunities than a matter of a lack of plot.
The best adventures have a twist. In the future, whatever the PC's are told is happening should be wrong in some fashion. At some point they should recognize that they have been misinformed (deliberately or otherwise) or have drawn the wrong conclusion and find the adventure goes off on a new tangent.
If you can't think of a good twist, or you want your twist to be playing the scenario straight (if players have gotten to the point that they expect a twist), try to remember that everything can be diverse and have backstory. Obviously, you aren't going to have RP if every monster the PC's meet attacks immediately and fights to the death. Don't get over reliant on ambushes, as it tends to be a sign of DM ego investment. So have Kobolds negotiate, parlay, boast, or otherwise initiate RP. It doesn't have to go anywhere, but it's still good practice and it means that the foes aren't faceless. That cowardly but boastful kobold chief that's been tormenting the party eventually gets his well-deserved comeuppance, for example. It's always more satisfying to defeat a foe with a name and a history.
Beyond that, stop thinking of intelligent monsters as having lairs, and start thinking of them in terms of villages. What economic activity do these creatures normally engage in? Who are their trading partners? Who are their enemies? Kobolds could have slaves, allies, and prisoners - each of which might have their own reasons for wanting to engage the PCs. Slaves want to be freed, or even to take vengeance on their former masters. Allies like ambassadors and merchants might want to negotiate free passage out of the conflict zone. Prisoners might want to be rescued and returned to their homes. Sometimes these might make for very unusual encounters and strange alliances. A slave that might be normally of a monstrous race the PC's would kill without thinking, might be a temporary ally.
There also can be neutral factions even within the kobold civilization. A blind lizardman shaman might be honored by a tribe of kobolds whose affairs he doesn't always approve of. Cave dwelling fairies might be hostile to neither their kobold neighbors or the PCs provided they aren't provoked. Abandoned sealed off areas of the kobolds home might house the ghosts or haunts of former victims, who don't necessarily hold the PC's as culpable or at least engage with the PC's first and before they start terrorizing them. And so on and so forth.
