You would do yourself and your clients a favor if you don't allow them to spec Solid colors for 4/c jobs. If they spec a color that is not achievable in 4/c, they will be disappointed, and blame you for the lack of color match.
That being said, if you never print spot, you don't need the books. If you rarely print spot, then the need for a new solid book depends on how color-critical those few spot jobs are. If they are not color-critical, you may get by with the old books, as long as you explain that the colors may be off a bit. I'm too picky to go that way, but it may really not matter much to your customers.
and of course the new books also have the new colors...
people still request pantone colors not realizing that almost everything prints process...
Basically, I'm on the fence regarding getting the pantone solids books
I think designers often use the Pantone system as an alternate to color management, and that would work if they were always printing solid inks which of course they are not. So we see many threads about Pantone colors either printing or displaying incorrectly.
The Pantone Bridge colors are single CMYK process builds and how closely they simulate the solid ink printing in Pantone's solid ink formula guide, depends on the 4-color press conditions—the color builds are device dependent. It isn't clear what device or press conditions the Pantone Bridge colors target, but I would bet it's not your Ricoh 651EX. So you could print a Pantone Bridge swatch chart from your Ricoh 651EX and reference it rather than the Pantone solid swatch book and get more reliable color.
The alternative is to make color managed conversions from the Pantone Solid+ Lab (device independent) colors to your press profile. Whether that works depends on the accuracy of the press profile and the understanding that some colors or considerably out-of-gamut. Also using Ink Manager's Spots to Process to make the conversion can be problematic if the color is a tint. See this thread—Re: Ink Manager Bug/Problem?