Just to clarify, plinths are simply the bases for the speakers and are standard with the spikes (which you can use or not use at your option). The base price is for painted MDF plinths. If you would like matching or contrasting wood plinths, you simply pay for the additional cost of the materials used.
As for grills, normally I only use grills on the woofers where the frequencies concerned are not an issue. I do not personally prefer grills on the midrange or tweeter since I don't feel there is any such thing as "acoustically transparent" grill cloth.
That said, upon request, I will try to provide whatever grill arrangment is requested. It is somewhat problematic doing the type of midarange/tweeter baffle I do on the HT3's and incorporate grills in the equation.
I like to use magnets to attach the grills. That way there is no visible evidence when the grills are removed. This is not a problem in the woofer area since the magnets can be embedded in the cabinet before the veneer is applied.
But with a solid wood baffle (or MDF for that matter), the magnets would have to be installed in the baffle before it is attached. This means drilling in from behind and stopping very close to the front surface. Any mistake and the baffle would be ruined and a new one would need to be created (costing time and materials).
For this reason, I normally recommend that if grills are required for all drivers, that the additional baffle for the midrange/tweeter be eliminated. After all, this area of the cabinet is already 1 1/2" thick.
Will there be a difference in performance? Yes, you could certainly measure the difference. Will it be audible? I have never been able to hear it. And it is certainly far less problematic than the grills themselves.
One additional benefit of not using an additional baffle on the midrange and tweeter is cost. There is no additional solid wood required as this area is veneered either way. You simply end up with a flat front veneered panel.
I hope this makes sense.