Hello, I'm a Megadrive fan too
As many of you, I was disappointed with the image quality on my LCD TV.
I've recently discovered and bought the expensive "XRGB mini" device.
It's an hardware upscaler, basically, it imitates the CRT TV rendering (scanlined) on modern HD TV. You just plug the Megadrive scart cable in the XRGB, then HDMI cable from XRGB to the TV.
The result is amazing: it even fixes some issues I had with other consoles (European Saturn) connected directly to my TV (e.g: black screen, lost synchronization ...).