SSD drives are already at sufficient size to replace traditional HDDs in many circumstances. It boils down to, "What is your purpose or requirement?"
For me, performance gains drove my purchase of a pair of X25-E drives for home use, and a company purchase of dozens more for the laptops at work. My personal use was to speed up Windows and the load times of applications. The 32GB is plenty of space to operate from in most situations. SSDs are not yet the best choice for "static" data storage such as movies, photos, etc. when you compare the cost. They are engineered or marketed as performance drives in most cases. So, servers and high-end workstations would likely benefit the most, but any home computer where some extra speed is wanted will certainly benefit. I strongly recommend the X25-E series. They are more expensive, but they are super, super, super fast. It's a purchase that won't be regretted -- and you can still install those cheap 500GB or 1TB drives as secondary storage for additional data.
So, let us know more detail about what you have, and what you want to improve or upgrade. Then we can better answer your question here.