While I agree that some may benefit more than others, I don't think that precludes anyone else from seeing some benefits.
This sound rather silly, but we don't need cell phones cause we can user our home phone or just wait till we get to work, we don't need washers and dryers, we can just go to the laundry matt. The original poster is considering getting an SSD and asked about the benefits. They also asked if they got a regular HD and then wanted to change it later. So, it boils down to what someone wants and if they would see any benefits and the answer to that has been made very clear by multiple posters. They didn't ask if you thought they should get one or not, they can decide that for themselves!
Your experience or opinion isn't anymore right than anyone else's on this subject, so don't even go there. My experience on the subject would indicate that I've seen great benefits and I am happy that I made the purchase. No one in this forum is going to tell me what I know to be true for me. I suggest others find out for themselves and let there experience speak for itself.
No no no no no, that's completely different.
I understand you saying that, if somebody asks if it's beneficial, we should tell them, but in THIS CASE, one in which you obviously, again, don't know what you are talking about, he will not benefit if he doesn't need the darn thing.
Your examples (and by the way, analogies aren't logical arguments; just for future reference

are based on things that are somewhat necessary in today's life for convenience. It isn't so much a washer and dryer so you don't have to drive 10 minutes wasting gas, having a SSD opposed to a HD is more like a sports car instead of an economy.
If you're going to use analogies, at least pick correct ones. Sports car gets you there faster, but if you're staying in the city, you won't be speeding much.
On the other hand, if you're going on the highway a lot (analogous to large files in case you're lost), the sports car would get you faster if you drove recklessly.
My point being that you don't need the SSD at all, if you aren't loading a lot of files constantly, the benefits won't be noticeable and you'll have effectively wasted money. Yes you get the security from drops and the sound is quiet, but simply relying on speed in this sense as a premise isn't very smart.
And I'm not saying you're wrong, I'm saying that you're basing your argument around something that, with the price and size constraints looming high over head, will be washed out if the user isn't doing something that requires it. It's basic knowledge.
Do you put a turbo in your car? No, why would you do that?
Do you put racing tires? What about lowering the suspension?
Weight reduction? NO. Why? Because you don't need it. The benefits (better performance) would be outweighed by the cost and the fact that you "wouldn't have a real reason to use it."
I'm just advocating rational spending here. Yea if you want to, hypothetically, throw money away, sure, go ahead and get the SSD if you don't need it. You could then argue the fact that the user must then do things that take advantage of that extra couple hundreds of seconds faster.
Do you use keyboard commands? What about better touch tool? I could argue I get a lot more done on my machine with the stock HD than you do with the SSD. You also have to think about HIM and how he uses the computer. If he just clicks on icons, the time it took to click rather than to type would offset the benefits of the SSD.
There are so many variables to think about; don't just suggest what you like and bash others who offer an opposing argument.