does it logical to invest on expensive transport?

There are a number of very high quality cd players on the market with digital inputs so that they will function as a dac too which eliminates having to choose. I find and recommend to my clients not to eliminate any medium but to embrace them all and move forward with the medium which you enjoy most, for some that is CD, some vinyl and some computer audio - it is nice to be able to enjoy them all though.

***dealer disclaimer*****

Some examples are the Esoteric SA-50 which has USB, toslink and coax inputs, an extremely high quality transport and plays CD and SACD.

Another example is the new Marantz UD7006 blu ray player which although it does not have a digital input will act as a streaming device with netflix and other mediums and sound very nice for it's price level on cd/sacd.

NO!$$$$$$$

I have in my collection over 7500 hundred redbook CDs, which I'm not going to download into a hard drive, therefore, my investment in a reference transport made perfact sense to me.

If you don't have a large CD collection and down load your music into your hard drive or music server, then a very expensive transport might be a silly way of using your resources. I also ran the experiement just to hear which still offered better sonic performance a great transport or a hard drive and still believe that my reference transport sounds better in my system with my DAC.

it's all relative to how much money you have or your intensity of interest

Logical? Maybe, or maybe not, and I agree with Larryken. It depends upon the level of your system. IME, a transport is even more important than a DAC, and a computer is a transport FWIW. At 15k you are at the end of the line where computers meet high end transports in performance. I'd opt for the computer, because it will be much(5-10x) cheaper. I wouldn't be surprised if the right transport could best the best computer set up though.

It might not be long before computers catch up though...