Hi jarakal,
I'm not exactly sure if we can follow this since we're on the private server but as far as I'm concerned, no it does not give you 30% more success rate, please refer to attached table.
I got this table from
http://iris-wiki.gpotato.com/wiki/Enhancement
and since it's from retail iris, i'm not sure if GM made any changes to the rates so..
Either way Shining = High Class and it does give you a higher chance of success but the difference is really not so significant.
Regards, Natsukii