More exclusive content and additional network features would make the paid service a better sell.
That being said, if any exclusive content being distributed through Plus was worth subscribing for, it's pretty reasonable to say that SCE would probably rack up a lot more sales and revenue by selling the content separately as well. The occasional (or even weekly) dynamic theme or avatar icon pack doesn't really cut it as exclusive content either.
The downside of Plus is that a lot of the free content being distributed to subscribers is NOT exclusive content and is typically material that has already been available through PSN, often for quite some time, which brings us back to the reasonable argument that if something that is now being given away with the Plus service is worth subscribing for, odds are you already bought it unless you're relatively new to the PS3 and PSN.
Over a year, there's no question that subscribers will have downloaded several times what they paid for their subscription in free and limited license content, but maybe the question that should be asked is whether subscribers would have downloaded even half that content had it not been included with their subscription fee.
End result: if you want the most out of your paid subscription, play more PS3 games (the Plus content) and basically use your PS3 more to get better mileage out of the subscription. The same thing applies to XBL Gold. You're more apt to play online if that's the main thing you're paying for with your subscription. Not too many people keep their paid subscription so they can play online once every week or so.
But overall, Plus is not a bad service.It gives paid subscribers extra content where as Gold simply takes away the basics from regular subscribers (no online play, 1 week delay for demos, etc.). It would just benefit from better network communications tools (chat, etc.), which is something SCE really doesn't need to charge for as an "exclusive" service anyway.
