I don't think there is any pressing reason for you to upgrade to version 9, unless you have new hardware which doesn't work with sme8.
I would disagree and this is why
- Included softwares in sme8 repositories are really old , I have in mind dovecot which is used for sogo. Sogo now use dovecot 2 and the version available for sme8 is dovecot 1.1. Of course you can do a hack but it is not safe.
- There are some new features in ibays for example with a new panel available with a contrib smeserver-webhosting...specific to sme9
-Versions of sqlite, python, mysql are more recent, and you can simply install PHP55 or PHP54 (need to be tested a bit). These versions could bring new contribs not realizable with sme8.
Of course, maybe we can find other reasons to keep or to leave sme8