A number of changes to Strava and MongoLabs meant the x2G app stopped working last year. I thought I would have a new app out that absorbed the main functionality of x2G however that is taking longer than expected, so I went back and fixed the number of issues it had. So it should be working again!
My new app will synchronise to-and-from Google Calendar so will be a natural progression when it comes out.
As for Nike+GPX, I don’t use Nike+ anymore so didn’t notice it too had some issues which I see a few people have written updates to handle. So I have made it open source on GitHub now (https://github.com/jkili/nike-gpx), I should have done that a long time ago. So please feel free to keep the plugin up-to-date and I will post updates here when required.
Update 16/Mar/2016: NikePlus Plugin has been updated in both the download link and Chrome Web Store to v0.48 (Thanks to Per Jensen & Matthias Hüller). GitHub also merged.