I opened my Platinum file again after leaving it for some time. I went to the Top Trainer Cafe, and fought Gardenia, Wake, Candice and Mira there. After that I went to the villa to buy some more stuff. I bought the Bookshelf and Rowan came visiting and gave me a few books.
After that, I decided to try the E4. The post-National Pokedex E4 on Platinum is much harder than in Heart Gold, which is both nice and annoying since my team on Heart Gold is higher leveled than my team in Platinum. Like, Lucian's team is roughly on par with Lance (with their highest level 75).
Anyway. The E4 wasn't really hard, but I did get into a few troubles. I knew Cynthia's Garchomp would decimate my team, so I took time to set up. While Spiritomb was out, I used Gliscor to Swords Dance three times and healed. After that it was pretty much Earthquake slaughter. And my Gliscor was faster than Garchomp albeit being 4 levels lower. But I'm not complaining