In my view, scopes under 100 MHz are pretty useless...
That's an extreme statement. Basically you imply that having a 70Mhz DSO is about the same as not having a DSO at all. My 60Mhz TDS210 served me very well and I would keep using if I could.
Too much focus on equipment and feature list IMO rather what we design build and learn.
Well, I did say 'In my view...'. MY projects are all digital or very low frequency analog, VERY LOW frequency. Watch it on a V-O-M meter slow. All of my digital projects run over 50 MHz even though the external signals seldom get over 20 MHz. So, yes, anything less than 100 MHz is pretty useless if I want to be able to display something that looks somewhat like a square wave. In some cases, I really do care about setup and hold time relative to the clock and that's a lot easier to do when square edges look square. I have no interest in RF and even less in audio. Again, "In my view...". Other opinions willl vary.
Features are the entire reason for buying a DSO. DSOs will never be the same as analog scopes so there had better be some reason for all the interest. In fact, it's the features! Single shot, infinite persistence is one. Measurements is another. It's all about the features...
There are plenty of fine analog scopes on the used market. I bought my 485 via eBay about 12 years ago. It still works well. But it has no features and, again, for my purposes, it isn't overly helpful with only two channels. It's fast but it doesn't have features.
In the end it gets down to price. Sure, I'd love to have a 500 MHz Keysight MSO but that's not realistic for my level of interest in this hobby. What is realistic is a low end scope with decent bandwidth and features. Plus 4 channels. If I wasn't gaining channels and features, why bother?
Of course I can get by with less. I've been doing it the hard way for decades. But the capabilities of the modern DSO, even an entry level version like the DS1054Z, make buying a DSO very attractive. Attractive at $400, maybe not for $1200... It's just a hobby, one of several.
Sure, the 60 MHz TDS 210 is a good scope. Nothing wrong with it! But, realistically, if I couldn't buy one for $100, I wouldn't bother. Even then, I would want to compare the feature list against the DS1054Z and see how they stack up. Prices on eBay are all over the map but tend toward a number where I would just go for a more modern scope. The 210 doesn't do anywhere near as many measurements as the 1054Z. Nowhere close! So, maybe $200 for a used 210 or $400 for a new 1054Z - that's the fundamental question. OTOH, if I had the TDS210, I might not be looking for an upgrade just yet. It does have some features. Record length isn't one of them...
At this point, I'm pretty down on recommending used scopes. Some of our members have had less than stellar results. I'm happy with my $200 Tek 485 but I think I just got lucky! Others have had different results.
It's pretty easy to recommend 100 MHz as a lower end because it comes in such an inexpensive package along with a ton of features and 4 channels. Of course I'm going to recommend the DS1054Z or something similar. And, at this point, I'm not going to be recommending used scopes at all.