This question needs context.
Soft plastic will not last long on a drive train axle which has the wheels (gearboxes are probably fine though). It also will not last on axles which bear a lot of axial/side loads. The plastic will wear eventually.
I only bring this up because this is the reason our first regional in 2011 should have been GREAT, except for this exact problem on the drive train. We replaced the spacers with aluminum and our 2nd regional was our best ever up to that point in our history. Since your team is only signed up for one regional, you'll want to get this right
.