Dynamic range (number of bits for radios) is nice to have but not required for a great ADSB system. If you set the gain correctly with a 8bit receiver (RTL dongles) you can see both far away and close by planes.
The main thing to remember is that the software and hardware matters a lot in radio systems. A correctly adjust 8bit radio can beat a badly configured 12bit radio. Also the difference between a correctly configured 8 bit and 12 bit system isn’t much. Something around 10% more messages for 12 bits. This difference isn’t due only to the extra bits but also other components used in 12 bit radios which are usually better.
Dxista, thanks for posting the prices and links to the radios. The prices going from 8bit to 12bit radios are in the 4x-5x the cost area. The prices are dropping with the air spy originally going for around $200 and the new mini around $100. These higher end radio can easily be the most expensive part of your system while also not giving the best performance per money spent.