yes PLEASE don't do it half way - if you have to save up the $$$ - then save then do it right. You won't get the full benefits of new springs (handling, life span & ride) if you don't do or don't have fairly new struts. Worse yet you can amplify other handling & ride related issues. Just save your $$$ and do it right.
While some people feel that they can get away with just changing one thing and not the others, I strongly disagree. If you don't change out everything as a working system, then you will be needing new shocks and struts sooner than you think- and that will probably happen when you are not prepared to take the hit on your wallet. Your old shocks and struts will not be responsive enough to accomodate the lower springs, and they'll just get destroyed. And yes, it can even be unsafe. Listen to these guys. Save your money, or buy everything piece by piece, then install all of it when you're ready. Besides, why do two installations instead of just one? The aggravation is not worth it just to get a 'lowered' look the cheap & fast way.