CS influence: There are CS quests to find NW's or other civ's land, but more importantly, the more civs you know, the more likely you are to get random hits from connecting resources etc. that you would be doing anyway. I personally think it'd average out well for an exploring Spain. As for the gold from honour, any civ that took honour like say germany (FT went second) etc. could get that - it's a SP not part of the UA. To get it, you had to give up SP's elsewhere.
River attack - Sorry I didn't explain well. I don't like it because of Askia's army mix. There's lots of mounted for the UU, which do hit and run attacks and don't work over rivers cos they lose the movement and ability to retreat. There's also lots of ranged, because it's the best line and everyone has lots of ranged, which nullifies the river. The bonus is really for standard melee but it doesn't make sense for the Songhai to have a lot of it. They could have a more balanced army under the pretence of the river bonus for melee being a reason in itself, but then you feel like you aren't getting the most out of anything that the Songhai do.