You must have a bad Action Replay if you still need to swap discs for imports. I've played dozens of JP games on my US Saturn back before I got a JP Saturn, and now that I have a JP Saturn I've played tons of US games on it with the Action Replay Plus.
I did get a JP Saturn Model 1 because there are a few games that won't run on a Model 2, and there are a few JP games that won't run correctly or at all with Action Replay Plus - those games in my experience being Kyuutenkai Fantastic Pinball (won't run at all on a Model 2 regardless of region) and Real Bout Fatal Fury (also won't run at all on a Model 2, but even if you run it with AR+ on Model 1, there will be a few characters that glitch out heavily because the AR+ won't properly switch to 1M mode, so it seems to still need a proper 1M cart).
There's also KOF'95 and Ultraman: Hikari no Kyojin Densetsu - these games require their own unique RAM cart and won't run without them.
But yeah, aside from those instances (I know there's a lot more JP games that only run on Model 1 Saturns, but that's all I've encountered thus far) I've been able to play most games with my AR+ regardless of region.