Most PV schemes are grid tied, this means that the systems rely on a functioning grid connection to work.
Such schemes may be justified on financial or enviromental grounds, but most do not give any protection against blackouts.

An off grid PV system with a battery bank, does of course protect against blackouts, and even a small 12 volt system can be very useful.

There is always 'more efficient' photovoltaics coming... when n% efficient arrive, (n+5)% are 'just around the corner.'

Its not so much the lack of efficiency, but rather the high cost, that makes PV solar uneconomical.

Abosolutly, sunlight costs nothing therefore it does not matter if it is used inefficiently.
What does does matter is how much power is produced for a given investment.Therefore a reduced cost per watt is desirable, not a higher % efficiency.
Efficiency only matters if limited space is available, in most cases though the limiting factor is not roof, or other space, but money.

Even if you don't like the time it takes to pay off a PV system do look into solar water heating. The initial investment is much smaller and the payoff times much shorter. There are areas, like the far north where freezing is an issue eight months out of a year, it doesn't make sense without making the system complicated but for much of the south and west even very basic systems can pay themselves off in a very short time.

PV isn't the only game in town.

Efficiency would have a direct bearing on ROI.

How long will today's solar panels last? Is there maintenance/upkeep involved? If so, is the associated cost figured into the ROI estimates?

15-28 years