The only Platinum trophy I have is in Hyperdimension Neptunia Victory. I got most of the trophies on my way to getting all 3 endings, and the only other ones I needed were from maxing Lily Ranks (essentially relationship values that increase by making characters partners and having them fight like that). All it took was some grinding, and boom. Easy Platinum trophy.
I normally don't go for all of the trophies. It's always a bit too tedious, or involves doing things that I don't want to do. For example, I would try for BlazBlue CS: Extend's Platinum trophy, as I've already bested Score Attack and you don't need to beat Unlimited Mars mode, but it requires pulling off combos that I don't really have interest in learning, and it involves using the online mode, which I would not touch with a thousand foot long pole. I hate competing online unless I'm on some sort of team, like in Team Fortress 2. Especially in fighting games, where going online is NOT good for my self-confidence; I always get stuck at the point where matches are either too easy to be interesting or too difficult to be fun, and facing CPU opponents stops being a matter of learning and starts being pattern recognition that I can't apply to other players. Except Smash Bros. Brawl. I had some great matches with friends a few years back.