The gold plated pads don't oxidize, so they will have better contact with the MSX slot (and therefore less glitches). This will also increase the lifespan of the cartridge board.
About updating firmware ; What kind of adapter can i use to plug my USB Blaster on AS slot ?
You just need the 2x5 jumper pins and no soldering at all. The UB's connector is female, so you can unsert the pins into the connector and stick the other end into the board. When programming, tilt the connector a bit for better connectivity. Here's an example how I upgrade firmware:
