I'm running wobble bolts and they're perfect. 4x98 to 4x100 is only stepping up 2mm. There won't be any issues what do ever. It's when people want to stray too far away from the original pcd, that issues crop up. Example 4x100 to 4x114 or something. As for your wheel and tire setup conundrum: you can easily find a mesh BBS style wheel, in a 15in 4x100 wheel. To be honest the tire specs determine the "look" more so then the wheels. I'm not a huge fan of 15a in X1/9s either and IMO choosing a very low profile tire is a must. That being said, I had to make the jump to 15s due to the lack of 13in tire sizes available. Im currently running 185/45 Nankang NSlls all around. The outside diameter (with a now 2 in larger diameter wheel) is 13mm less then the 13in wheel/tire combo that was previously fitted. Going with 195/45s would have increased the overall diameter, slightly. Something like 9 or so mm. To my eyes, any larger tire such as a 195/50, or 205 or 225 just won't look fit to the car. Again just my preference. I may install 195/45s in the rear, at some point as there is still a bit of fender gap on the rear that can't be dialed out with suspension adjustment.