I recently picked up this scart switch. I cannot see any difference in the video image, between going through this guy and going direct to the OSSC. The general consensus is: if it’s a cheap scart switch, you get what you pay for. But, i believe this one is the exception.
But of course, if money truly is no object, then there are plenty of high-end SCART switches with matching price tags.
For the SNES jr., you can do a simple THS7314 or THS7374 based amp board. Voultar’s is THS7374 based. You may also want to consider the dejitter mod. It’s pretty much necessary, to get higher line modes, unless your TV and or capture device are extremely forgiving (most are not). Sold here by VGP.
The N64 will also need an RGB mod if you do go that route. It does not output RGB natively. The capability is there, the video amp is not. Tim Worthington has great N64 RGB boards, which include a deblur feature. Possibly the same place that you’re looking to for the NES mod: http://etim.net.au/n64rgb/.