Will have to say " it depends ". Just how far do you want to push your renders ? In your model I posted back I applied a Bevel Modifier to a few of the materials in the Deep Material Editor. Very few objects in real life have an infinitely sharp edge and the Bevel Modifier allows the render engine to give the appearance of a bevel to the edge of materials for a more realistic result without having to physically create bevels in your model. An example is all the trim in your models ceiling, quite a job to have to create a bevel on all the edges in the model, very simple to apply the bevel modifier in Twilight’s Deep Material Editor. Only you can decide if the price of Twilight pro is better suited to “your” needs. Personally I feel it’s a very good value for the money. Again I"ll say it’s well worth the time spent on Twilights forums, not only for learning but also to see the quality of renders being produced by other Twilight users.
OK, cool, if that’s all it is I won’t worry about it yet! Thanks again! I can’t tell you what a difference your help has already made. 
Hey kinda late for this, haha, but I thought I understood at the time, but now I’m digging back into my model again, and I want to clarify - are you referring to applying the Sketchup material paint or the Twilight material?
And exactly how deep do I need to open the groups/components? All the way down to the actual bare surface? Those cabinets are going to take forever, if that’s the case! 
I’m assuming the issues come from painting a whole group of component at one where the texture will map arbitrarily. If its a solid color it wont make much difference if any. But if it were a wood grain, you would need to apply to each surface separately in the direction the grain would be running so it looks correct in the way it would be built. This would need to be done in sketchup to establish the correct UV orientations and will be reflected in the renderer too.
Hmmm… well, that seems intuitive. The only wood grain I have in my model is on the floor, however, and I haven’t even been including that in my renders so far. The cabinets are all just painted.
And to be honest, the cabinets actually look OK.
The materials I’m struggling to get looking good is the marble countertops - I can’t get them to look like anything other than black tar - and the stainless steel appliances - they look bizarrely twinkly - even after removing all the materials and starting over (and making all the other corrections suggested here).
And I just missed Twilight full version going on sale for nearly half off! I noticed yesterday, the 16th, they had a sale “until the 15th” of Feb… 
That sucks that you missed the deal !!
Anyway, as I said, i think your cabinets are one solid color so its not important, but if you see attached, how problems occur with textures when applied “en-masse” to a group with a number of faces.
so its best to adjust the textures to each face so the grain runs as expected.
2. you may need to add some mitres to also give a more realistic appearance.
3. Also SU will tile the textures across faces giving an appearance of a continuous sheet of material, which also doesn’t look real, so some of those faces are best moved around to give the appearance of different sheets
As for the countertop I would give your material a lot of reflection and then add 20% roughness?
drecrego, In an earlier post I mentioned painting groups or components without opening them for editing because it is not a good basic SketchUp modeling practice. It also can occasionally lead to unusual results when rendering. Even solid colors can give unexpected results sometimes depending on the render material template and render settings used if painted on the “outside” of a group or component.
What material are you using for the countertop in your SketchUp model ? What Twilight material template are you applying to that material ? What material are you using in SketchUp for the appliances ? What Twilight material template are you using on those. What is your final light set up in Twilight, i.e. , Sun & Sky, Point Lights, Spotlights ? How many ? What Twilight render settings are you using ? Posting a picture of your render results can help trouble shoot also , a lot less guessing.