Is it important to long demo or own HIGH END gear to have a fair accurate view about it?

All other variables being the same, not necessarily. IMHO, long term is more about deciding on preferences, not figuring out how something sounds. Sometimes you just have to make your best guess, put down your money, and live with it for a while before your know if you prefer it or not.

So many times I have bought something, decided on the sound and put it away. Then I will doubt myself, get it out months later, and yes, it still sounds like I remember.

As one audiophile's wife said "They all sound good, just pick one".