First off, one of the main aims of conservatism should be the choking off and eventual death of the leviathon to its smallest possible level. This is something that doesn't take a libertarian.
Of the things that you mention, defense and roads are the only things that really fall under the federal baliwick, but even including the others, it is incumbent upon us as citizens to be certain that our efforts to fund government do not fall unequally upon the backs of any. There is too much power inherent in the ability to favor one group over another, and to allow envy and greed to dictate policy when "progressive" taxation becomes the method of funding our governmental largess.
Let's also keep in mind the effect of government-provided goods and services on the cost of those services.
When you break the link between the decision to want something, and the responsibilty to pay for it, you've triggered a runaway price escalation.
Big-government provides the illusion that something costs less than it really does, which drives up demand and prices for that good or service.
I lay most of the cost increases in our healthcare system at the feet of Medicare and Medicaid, and soon the new Presciption Drug Benefit program will just make it worse. When the recipient only sees 10% of any cost increase, additional demand and cost increases are guaranteed.
Government should be limited to providing only those services that make no sense for an individual to purchase directly for themselves. Like Defense, Judiciary, Penal system, etc. Even Roads would be less expensive if they were all paid via tolls rather than taxes.