There is no advantage without disadvantages and the same goes for a larger chainwheel.

Positives:

• Minimally more efficient, but if that were the concern the OP should first address it by learning to spin faster, which is more efficient both for body and bike.
• Slower wear - again, technically true but proper riding in the small cog, even at slightly low rpm's, involves very few miles of usage.

Disadvantages:

• Gear ratio increase - as shown in the chart earlier (and easily seen if one looks at percentage change) one needs to add 4 teeth on the chainwheel to equal 1 tooth difference on the rear cog.
• Front derailleur adjustment - The front derailleur must be raised and readjusted, often requiring a new cable.
• Flex - So much for efficiency, as a larger chainwheel will have a greater distance between teeth and the end of the spider, so will tend to flex a bit more.
• Chain length - to be safe in case of shifting to large large one will likely need to add links to the chain.

Of course if one goes the rear cog route it would not be surprising if a new chain is needed, but a new chain always feels so good, and in fact is more efficient.

A used crankset is unlikely to have more than 52 teeth, for only a 4% increase in gear ratio, or about 1mph greater speed at equal rpm's. Even the 53 tooth just adds 1.5 mph. It also may not be compatible with the current BB/spindle.

I know, the OP says he's not "comfortable" pedaling faster, but that can be learned in most cases. Admittedly we don't know what his rpm's are now or what physical limitations he may have, but if we assume he's pedaling at 90 rpm he only needs to up that to about 100 to add 2.5 mph or more to his top speed with no change in gearing. In the bargain comes better heart exercise, greater efficiency, lower drivetrain wear and in most cases a further increase in averatge speed as one gets into better shape.