Lots of interesting things to learn, but it isn't just 'plug and go' with one box that can see "DC to Daylight". Of course that teaches you about things like phase noise and how it impacts your ability to separate individual channels.
Fortunately it is well understood how to heterodyne DC to 200Mhz up into a range that these SDRs will operate. Lower frequencies are their own problem, the physics gets in the way. You get this for 'free' when you have multiple receivers running off the same local oscillator. There are interesting things to see when you have multiple receivers that are all running from a phase coherent local oscillator. Multiple inputs and outputs became a thing for me because I wanted to build an LTE base station, so I backed the LimeSDR and got one of those. For doing some bluetooth work I ended up with a band pass filter on the front end that killed off nearly anything outside the 2.4Ghz ISM band. You find yourself buying (or building) filters to knock back the US FM band, or a nearby TV station for example. But what if you can't hear what it is you are listening for? As digital devices the number of bits in your ADC really impacts your ability to deal with large adjacent signals in the band.
So more bandwidth, especially if something was using multiple "channels" in a space became key. But those sources transmit with a modulation and that modulation might consume a little (CW) or a lot (OFDM) of bandwidth. That suggested the wider the frequency range the more success I would have. My journey went as follows first I wanted to see as many different signals as possible from as many different sources as I could find. The truth is, depending on what you're interested in, any or none of those could be on your "must have" list. When I first started experimenting with SDRs I thought "widest frequency range" was the spec to go for, then it became "widest bandwidth" was the spec to go for, and then it because "highest dynamic range" was the spec to go for. Nice to have another MIMO radio in the mix.