Here's a few reasons why you should get a Windows Phone if you already have a Win7 PC and 360.
1. Office with Skydrive.
Skydrive is Microsoft Cloud solution I think you get 7 GB for free. You can download the Skydrive APP on Windows 7 and it will show up in your File Explorer.
With Office you can sync files between your phone and PC good examples are
- One Note sync your notebooks between PC and Mobile
- Excel if you like to work out I edit my workouts on my PC take my plans on the go on my phone and edit it @ the gym
- Word you can keep a copy of your resume on your phone and e-mail it on the spot
2. Microsoft Live
- Windows Phone will automatically sync your contacts and calendars to your Microsoft account so if you loose your phone or get a new WP your contacts will sync up automatically.
3. Xbox Live
- You can chat with your friends on Xbox Live
- Earn achievements on WP Xbox Live games
- Play games on your phone and continue on your Xbox 360. Only some games have this feature.
4. Music
- If you pay the extra 10$ you have unlimited music downloads from the Zune Marketplace for up to 3 computers. I have mine synced to my Work laptop, Home PC and Windows Phone I can literally download any new album on the spot via LTE its pretty awesome. Or if you want to download a single you can find most of them on the Marketsplace.
I highly recommend upgrading your 7 PC to Windows 8 to make the experience even better.
About upgrades you aren't getting WP8 but I highly doubt your LG7 is going to get Jellybean. You will be getting WP7.8 which has the new start screen and Nokia will be releasing some really dope apps for your Lumia 710 for years to come.