As far as an SSD vs HDD is concerned to the average layman, you'll not see any difference with the SSD over the HDD asides from a massive speed increase. (plus cooler running and less noise)
But I wonder how much difference you'll see in a realistic, non written on paper sense if you are just using it as a storage device? I mean I know there will be a difference, but because it will be accessed so little in relative terms your perception will be different.
What you really want to do is run the SSD as your OS drive and use the HDD for storage. That's when you'll see the massive differences.
What you really want to do is run the SSD as your OS drive and use the HDD for storage.
Like I've said earlier, you use SSDs for whenever you need random access to be accelerated. So this could be booting or data (obviously depending on the nature of the data and whether it needs to perform lots of small/random reads/writes).
There's no hard/fast rule for whether SSDs will be of a noticeable benefit for the extra outlay over mechanical drives. If you boot your machine once for an all-day work session on a single application, then there's not much benefit in booting off of an SSD and you may as well use a mechanical drive (afterall, once it's booted & loaded into memory it'll unlikely need to keep accessing drivers etc) for the minute or so in the day you'lls save, on the other hand, if you're switching machines on/off rapidly or using multiple apps throughout the day then it will be of benefit.
The key is to finding the bottlenecks for YOUR system and how YOU use it.