The E-5 may seem costly at first, but you really do get a relatively great and (IMHO) very justifiable value for money. I had paid about $1500 for a brand new Sony A700 in 2007, and it was in retrospective a rather lukewarm, dust-grabbing toy compared to my snappy, invincible, and inspiring E-5.
The colors from the E-510 are not exactly like the ones you get from the E-5; I like both personalities, but will leave this delicate, subjective question for you to decipher. In any case, they can always be easily modified via WB settings, etc.
Just to add to all previous comments, the E-5 back LCD is very crisp and high def (usable almost everywhere and helpful for judging if more shots / retakes are needed). Its battery life seems to last forever. Framing through the viewfinder's huge pentaprism is spectacular, bright and precise. Greater balance with the 12-60mm or 70-300mm aforementioned may be another significative advantage. The AF will definitely be faster, and more efficient especially in lower light situations. The multiple shots function is cool and sometimes missed on other models or brands. If needed, there is a movie recording function. The double card system (SD/CF) is useful too. The built quality is impressive, really!
Not the same league maybe, but a Leica M9P body costs more or less $8000 + tx. For a good kit lens such as the small 35mm Summilux f/1.4, add another $5000 + tx...
With your already-paid-for 12-60mm gem, one of the best general zooms ever made optically speaking, the relatively cheap E-5 can also make miracles!!!