G'day, Shags, and welcome to
Kunena. I have moved your topic to a more appropriate category.
Thank you for an interesting range of questions. Most of your questions are answered by reading
K 1.6 and K 1.7 Upgrade Guide
and studying the links that are referred to in that document.
The "virtues" (as you used the term) of upgrading are:
(1) You will have support from this community when you upgrade. K 1.6.3 and any add-ons (including
Kunena templates) that you may be using - written by the
Kunena team or by other developers - are not supported and, if you continue to use them, they probably will not work with K 1.7.2.
(2) You will not "alter" or lose any forum posts.
(3) If you are using the
Blue Eagle template written for K 1.6.3 it will automatically be upgraded to the new version
(4) Any custom category images that you were using will not be lost.
(5) Layouts - I assume you mean custom templates or modifications made to Kunena 1.6 source files - that is more complicated to answer. It depends what kinds of layout changes you may have made. We have always advised members of the community not to directly modify
Kunena source files unless they know what they are doing, how to do it, and take the responsibility for maintaining those changes whenever they have to upgrade later on.
I have answered your questions in general terms and I hope that this information helps. For the most part, however, you should find that the actual procedure of upgrading from K 1.6.3 to K 1.7.2 takes less than a minute. The preparation time beforehand (reading the documents I have referred you to and upgrading other components that you may also be using) will take you significantly longer.