For your MQD calculations, check the rules about whether upgrading just a segment of a trip gives additional MQDs (and MQMs). If you upfare the ticket by paying the fare difference and having the ticket reissued into the higher (D1 or domestic FC in this case) fare class, of course it does count. Paying for an upgrade during OLCI generally doesn't. YMMV. In fact, you probably should check whether you've been given some MQDs where there should not have been credit, as there's a chance that DL could claw these back. I'm just saying that if you decide to go for the additional $1100 trip, you should be confident that it's needed and will work or at least know something about the risks.

Remember too that award tickets earn MQDs at the rate of one cent per mile (and MQMs based on distance and cabin class). If you have RDMs, you could use them for the $1100 trip instead of paying with money.

In the past, it was more expensive to buy status than earn it by flying. I wouldn't count on (3) being an option.