After living with the Intuos5 Small for a month, I thought I'd give an update.
The only addition the tablet brings to Lightroom for me resides in the brush and the rotary dial. Let me state what I couldn't find stated explicitly online, or what Wacom never answered in my written inquiry: The pen defaults to pressure-sensitivity when using the adjustment brush. This allows Flow to be numerically set at 100% in the LR Brush dialog, a setting I'd rarely use with a mouse. This permits stylus pressure to deliver 0% flow at minimum pressure, and 100 flow at "maximum" pressure. If your Flow had been numerically programmed instead to 49%, then maximum pressure would stroke at only a 49% flow. You could define minimum and maximum stylus pressure to instead deliver "full flow all the time" if you preferred.
The rotary dial, which I operate with my non-dominant hand, allows modulation of brush size or zoom ratio on the fly. This pen-dial combo is, for me, valuable in a way that a mouse or trackpad isn't. The programmable buttons on the pad itself, or the side buttons on the pen, haven't replaced what single keystrokes offer my workflow. The pad's gesture surface is nice, but I'm still reaching for my trackpad out of habit. Using the stylus to click and point, meaning unrelated to brush function, is OK and probably fine once your brain is trained to understand the "absolute mapping" of stylus location and screen location.
I can't imagine using anything larger than a Small Intuos, as pen movements would become very large in scale to cover the monitor real estate. In fact, I have experimented with calibrating the pad surface area to less than what's available on the size small pad with the goal of economy of wrist motion.
Stylus function in Photoshop is different, and grander, and it's easy to see why the Photoshop artists use these pads.
I'm enjoying the Intuos5 with Lightroom and imagine I'll continue to use it. I could not, through, claim to have found the pad as quickly irreplaceable as I'd hoped it would be. It is understood that the learning curve to, in particular, stylus location and movements makes incorporation of the Wacom into the workflow of the uninitiated (like me) not an over-night process. In no way to I discount the testimony of other users in their finding the Wacom Intuos of tremendous value.