Wow this is one of the very very early Subaru builds. We didn't use Outfront Motors for very long. Great motors, but we quickly changed to stock ECUs and USDM motors to simplify the parts catalog. There are a TON of updates to the Suby builds, fuel system and coolant system, but I am also a fan of "if it ain't broke"...
There are plenty of inline fuel filters and pre-screeners in 3/8", 5/16", 1/2", that are rated for fuel injection systems, check Speedway motors or various aftermarket diesel products, its common.
Your clamped fittings are all high pressure socketless and the clamp is a back-up, nothing wrong with them but also nothing wrong with updating them, just not necessary.
Surprised about the Outfront comment on sizing, as that would be the pump and fittings they supplied with the motor at the time. Likewise, I don't understand why someone would run a step up fitting to try and force larger diameter line when the fitting size is already a restriction and dictates the size...
The cars today (and for the last 10 years maybe) have 3/8" feed and return throughout, matching the donor components. The outfront stuff back then used a JDM top end and from memory is set up for 3/8 and 5/16 mix (or metric equivalent).
As for fuel line and age, we haven't seen long term aging issue with Gates Barricade hose, which is our standard, but I DO NOT know if we started using it back in '09 Best to do a physical inspection on your fuel lines. The ethanol content of today's fuel will dry out standard rubber hose quicker than expected.