If a 512+ SSD was reasonable affordable i would replace the internal drive. for now this will have to do. I assume thats why i did not notice this behavior in my 2010 server. the drives hold always be ready.
That's why I went for a Seagate Momentus XT in my i7, cheap and pretty quick. For $100 it's a cheap fast way of improving the system's performance without the SSD costs. Though I do understand you're not going to get SSD speeds but it's a massive improvement over the stock drives Apple supplies.