for a VPS no, a small Lowendbox, wont add a significant enough bad impact to the climate, so far my opinion.
Dedis mostly put them into idle and consume far less energy, still they consume a lot more than a single vps so I would say yes, even if they idle.
But like 30-50 Watts on idle wont have that much of an impact, but if you add all these machines that idle in datacenters it could be a significant impact.
So if you have a longterm idle machine e.g you got it for a cheap price and you dont need it.
May power it down for the weeks you wont need it? Would be a start.
But most of the people wont do that, since yea, you pay a flat pricing, you do not directly care, since it wont cost you money. So I would consider them impact of doing it not big enough, more people would need to do it but a good start.