I clicked and browsered my heart out but couldn't get the 50K bonus offer either-just the 30K, with $1000 spend. Got the card, made my $1K spend, waited until my statement closed and then sent an SM saying "I recently applied for the United MileagePlus BusinessExplorer card with 30,000 bonus miles. I've become aware of offers in Chase branch and elsewhere offering 50,000 bonus miles recently. I’d appreciate it if you could please match this offer."

They replied, "As you requested we have added 20,000 bonus miles to your account to match the newest offer you received. You will see this adjustment on your next billing statement." No mention of increasing spend.

Thanks Flyertalk!