Hi Martin,
to be honest it is sometime ago when I was using miniSAP or trial versions of ABAP based NetWeaver servers. However when it came to extend of my installation either by some SP or add-on I never succeeded. When I tried to import package via TA like SPAM or SAINT I always run into the problems during installation. Mostly because package needed some DDIC objects (like ECC (that time R/3) modules related ojbects etc.) which were not part of of original server installation.
I read on SCN's forums that newer versions of NetWeaver is possible to upgrade by e.g. Basis SPs but I never tied that. It would be great of someone form SAP could clarify the question whether trial versions of NetWeaver are upgrade-able or not.
cheers
m./