I'm not a never say never type of person, but after the back to back Coast to Coast in 2024, I will say this.
That was a very intense and exhausting experience. Over a 2 week period, I had 2 cross country flights, 2 6 hour drives to and from Disneyland, and then the whole 7 races in 11 days took a lot out of me. To be honest, some of my celebration after getting the Coast to Coast was more muted because I was so tired. I was so done with running during the Disneyland Half that I decided to keep up my pace once I knew I was safe to finish only because it meant I could stop running sooner.
My other 2 Coast to Coasts were in 2012 (Disneyland Half/Wine & Dine Half) and 2017 (Star Wars Kessel Run) and I feel like I enjoyed the entire experience more after spreading it out.
I think what I'm really saying is that if at all possible, it's best to try and spread out a Coast to Coast so you can better savor the experience and truly enjoy the parks. Fortunately, I'm a frequent Disneyland visitor so it wasn't that big a deal for me to "short change" Disneyland, but it is definitely a factor that people should keep in mind when doing the Coast to Coast and visiting the "other" park especially for what may be a first time or rare visit to the "other" park.