I don't have the reference in front of me at the moment but I have seen the listings. From the late 80's through the early 2000's CU was consistently in the top 30 for total football revenues. This included media revenues, ticket revenues, road payouts, bowl moneys, and other football associated revenues such as concessions, seat licenses, etc.
You have to consider that for most of this time period CU was one of the most televised programs in the country. CU also played a lot of major road games at high prices. The big differentiator (other than being in a good TV situation is that although the stadium is not large by BCS standards it was consistently close to full and at high ticket prices and substantial seat license fees, etc.
To say that we have been, and should be in the top 30 is significant. That said the gap between the schools just inside the top 30 and the schools inside the top 20 is pretty significant and the schools inside the top 10 have a huge lead. Texas, Florida, Tennessee, Michigan, Ohio State, Penn State, and some others make our revenues look like chump change. Even with that although CU is not one of the "Elite" programs, it is one of the big time programs and unless you were to cut out all but the top few CU would be included in the upper division of college football from a money standpoint.
In response to your ending statement I don't think that it is as much CU being higher in revenues in prior years as it is other schools revenues growing faster than CU. The Big XII media contract was not particularly favorable to CU in that it paid a premium to teams appearing on the major network slots and for the past 5 years CU hasn't had a lot of appeal in that regard. It was also an outdated contract well behind some other conferences. In addition while attendance at Folsom field has been fairly steady it has been inflated with seats sold at promotional prices.
With the combination of the new PAC media contract plus the reported additional conference contract money we should see a major jump in that area. If Embree and Co can bring the program back to respectability we should see the interest in CU ticket come back and see those revenues rise substantially. Either one of these factors takes your #43 ranking and moves it up at least 10 places easily.