The touchscreen is nice, major change in radio interface. Sort of like the jump from manual VFO dials to digital displays. Whether that's an improvement or not I guess depends on the individual, but I think it's appropriate for the FTM-400 because you can customize the display to show the important things in different modes, so station list, reply for APRS, squelch, reverse on voice, etc.
If it's in your budget the TM-D710 and FTM-400 are top shelf radios. They are fine analog FM radios, just all those extras are not free if you never use them. I happen to have an FT-8800 still, which was my first 'good' mobile radio in my truck. In some ways it's probably superior to the FTM-350 but the difference on voice is minimal. They both receive about the same, their transmission quality is indistinguishable to the other station.
The reason I say it's better is that the simple interface and no APRS means fewer menus to dig through to change stuff (like display brightness, the FTM screen is annoyingly bright at night if set high enough to see in daylight, so it has to be dimmed) and the face is smaller, thus easier to install.
I've said it before and will reiterate, the FT-7800 and FT-7900 are IMHO about the best example of a mobile FM radio as there ever has been. The interface makes sense, the buttons and dials are the right size, lit and clear. The radio performance is hard to beat. The price is right. But it's not dual RX, doesn't do background APRS, etc. That stuff is nice but understand that it can be distracting and clutters the design.