You're pretty much spot on here, but I'd like to take it a little further.
1. On the outside looking in the Dolphins appear to be in a good position cap wise. They have a total of $20m in cap space including Clay's tender and they have about $23M next year, but that doesn't include Clay's money.
In order for them to get to this point they needed to trade and/or release Ellerbe, Wheeler, Hartline, Starks, Wallace, and Gibson. Their safety from last year, Delmas, is not under contract neither is their back up QB Matt Moore and RB Moreno. Odrick walked away in free agency. Stills was acquired in a trade and he replaces Wallace. Even though none of those guys were really productive they're still bodies that need to be replaced. The Dolphins didn't naturally get to this point in their cap.
On top of that Ryan Tannehill will have a $15M cap hit next year if he's not extended before then. Vernon and Pouncey are also free agents.
They truly can't afford Clay. If they re-sign him at $7M per, then they only have $16M remaining to fill all those positions.
2. Cameron's cap hit is only $4.5M this year. I highly doubt they bring him back at $10.5 next year. This is my concern when it comes to Clay
3. Poison pills are no longer legal.