Warning: this might get long.
What's reasonable or fair comes down to what other options each side has. Can CU find another beatable team to come to Folsom 7 out of 10 years that will be a guaranteed sellout? Can CSU regularly schedule 1-1s with P5 programs that would provide at least one home game every other year and is sellout or close to it? The answers to those questions are probably not and try again later.
I've read every post in this thread and follow allbuffs semi-regularly, only really commenting on CSU-related discussion. I get that a good majority of CU fans on here are over this series and want it to end. I get not wanting to play "home" games in Denver. I get the headaches and frustration that come with dealing with an annoying opposing fan base. I think much of that is fixable.
I would propose moving CU's home games in the series back to Folsom while CSU plays theirs in Denver until the new stadium is ready. Guarantee that CU can be the home team in years where they have 4 Pac home games. Those are pretty easy changes IMO. The next one is not so easy.
Both fan bases contribute to the **** that gets spewed. I don't know who started it but both contribute to the cycle. CSU is little brother and is so irrelevant... CSU wins a game every 3rd year and then you never hear the end of it, at least in part because of the perceived arrogance/talk leading up the game and throughout the year... Wow I hate these CSU fans, I hate this series, go back to cowtown and be irrelevant for the year besides when we play you for charity... CU wins the next two years and it's I told you so CSU sucks, we are so much better, we play in the Pac 12 little brother and don't you forget it... CSU wins again and reminds CU that both squads have the same amount of Pac wins over the last 2 years... This series is stupid and if we stopped playing them it would completely ruin them... Good, if we stopped playing CU it would help our SOS... and on and on and on.
Both fan bases need to stfu. CU is in the dumps. CSU had one moderately good season, after being in the dumps, and who knows what future years will bring. There is absolutely no respect for the opposing program and fan base and it's ridiculous given the lack of success both programs have had lately. Neither program has anything to brag about. The arrogance on both sides is so undeserved it's astounding. Changing that starts with us as fans, and on both sides. In a way, that's what I'm trying to do here. We can talk football, be fans of our respective teams, and still realize that CU and CSU being good again is the best thing for everyone, both are decent schools, and both towns are different yet great places to live. When you strip away all the fan base bs there is little to dislike about the opposing school/program. We can (and should) still want our teams to win without demonizing the other one. It all comes down to respect.
I never really answered the initial question. I think both programs would benefit from being able to host a winnable guaranteed sellout every other year. I think both programs would benefit from working together to raise the profile of college football in Colorado. I think both programs would benefit from this series being continued (note: I did not say NEED, each would be ok without it too). Pushing for a 2-1 is likely to lead to the end of the series, with both programs taking their chances elsewhere. I don't think that's a risk worth taking.