I just went through it with my TC-24D for the first time at 310 hours. I too thought the oil looked like new, but when I had it drained in the 5 gallon bucket, it was obviously "worn". Heat and pressure breaks down just about any material and I would have to guess hydro fluid is no exception. If I'm correct on that guess, there isn't anything a new filter alone is going to do to improve it.
As you go down the check list in the manual, it also says to change the front axle oil and replace with hydro fluid (at least mine does). I considered skipping that part, but went ahead anyway and am glad I did. It was by far the dirtiest oil other than the engine oil.
Just a suggestion, I jacked mine up and removed the wheels to get at the drain plugs, filters, and fit buckets under. Well worth the effort. Pretty easy job really.
</font><font color="blue" class="small">( I asked a dealer and he said some people do and some don't. )</font>
My dealer told me the same thing. When you add up all the prices for the filters, the hydro fluid is relatively insignificant. I personally feel better knowing it has fresh oil. There will always be some old fluid left in hydraulic attachments, not much you can do about that.
Brad