A Solid Plinth purpose produced to expand the footprint dimension of a small footprint Cabinet Base, will offer a stability that the Speaker Alone will not offer.
The Idea of spending monies on a Plinth that serves only one purpose is one that can be looked into to further, to see if similar but alternative options are fitting.
There are Plinths that Expand on the Footprint and also offer a suspension platform for the Speaker, decoupling the energies being transferred and causing colouration.
I am a advocate of Speakers mounted on a suspension, and have been creating my own designs and been demo'd other methods, off which all are a substantial improvement for tidying up the sound produced.
The goal for a Speaker with a small footprint will be to workout which suspension Plinths are models enabling the Speaker to be fastened to the Base.
Additionally, there are simplistic options to be used, to add intermediate base that is coupled to the Suspension Plinth and not needing any modification to the Plinth. The intermediate base can also prepared to enable the Speaker to be fastened to it.
The use of suspension as a method of Speaker Cabinet support is one I very strongly recommend.