https://www.google.com/amp/s/www.to...t-specifications-motherboard-specs,40467.html
X570 is more than just Gen4, it's what it does with it. With B450 you share ports with storage and pcie x16, Gen3 and Gen2 mixed lanes etc. X570 is all dedicated Gen4, no sharing, full performance from the 5700xt etc.
And that's not including the extra ports, upgraded Amps on the VRM's etc. There's a few decent B450's that'll handle upto a 3950x, but that's pushing it close, for the 3700x and up a X570 is a safer option.
Is it worth it to upgrade now? That's iffy. I'm in the middle of workin on my new build and Amazon is wanting almost $700 for an Asus X570 mITX, a $250 board at newegg (out of stock, figures), the $113 SFX shot up to $189 before going out of stock, so with Covid-19 creating issues with shipping, essentials and priority shipping only at times, shortages of stock etc, there's plenty of price gouging happening. "Oh, I'm stuck at home for the next month, time to upgrade the pc! (oh, quick, let's jack prices up because ppl are stuck at home and will spend money on upgrades now! )"
Worth it? I dunno.