Tbh, I think a new resource (or Wonders) would really get things moving. Not gonna suggest one since this isn't the place, but I thought I'd throw the idea out there :P
Also, maybe give tech a cost reduction after it drops below the max purchased (similar to the way infra and land work). Doesn't need to be 50%, but it would make the most destructive war a bit more of a competition (ie, in Rd 27 I think the there was a near 20k difference in between 1st and 2nd place)