We both agree that money will not be lost on investing on the Sea Cow or the Fairground Mixer.
The question that Ed asked was what would you invest your money in, if you're taking it out of SSDs. I'm thinking long term, not short term investments. I do agree with you that short term, this is not the place to put your money. I will also agree that ToO is a good set to invest in, and buying 4 ToOs with the money from 1 SSD is not a bad thing at all - if you sell SSD at $750, invest another $50, you've taken $450 and turned it into an $800 investment quickly. When both were available at RRP, I considered which was the smarter investment - 2x ToO or 1x SSD. Although I put the money into an SSD, I seriously considered 2x ToO to be the better investment long term.
To answer your question about the Sea Cow and Fairground Mixer, I will use one set to answer both of these questions: 10196 - Grand Carousel
Sea Cow - I didn't like it; until I saw it in person. Then I was blown away. This set is flying under the radar IMO. It's routinely hard to find, and routinely sells above RRP on eBay. Ship completest will want it. Lego Movie completest will want it. It's honestly a really awesome looking ship. I'm not a ship collector at all, but I have one in my personal collection (not yet built), because it's just that darn cool looking.
Sea Cow and Grand Carousel were both $250 RRP. I remember looking at the GC, loving it, but never buying it (I was still in my dark ages). I remember thinking, "who would pay $250 for a LEGO set?" Eight of them sold in January on eBay, with an average price of $2,100. Nearly 10x RRP. Am I suggesting that the Sea Cow will hit 10x RRP? Of course not. But I do think that these sets are very similar in appeal, value, and availability.
Fairground Mixer - you ask the question, "who is your target buying audience for that?" Let's the the obviously out of the way first - the same people who would by GC. But, it goes beyond that. LEGO Group clearly thinks there is a buying audience - we've got a new Ferris Wheel coming out later this year. Those two sets will compliment each other very well. On top of that, you've got the Joker's Funhouse set (retired last year), Joker's Bumper Car (2015), and the new Jokerland sets. Together, that's a pretty decent "county fair" theme without even trying. Maybe that's a stretch for most people. It works for me.
But, I think the FM is another set that is undervalued and underhoarded at this time. It's another set that's flying under the radar. And, if TLG is starting another major, yearly theme (a la Modulars), then FM is the first of the theme.