Please don't rebuild the engine. I have 5 Subarus and only one has less than 200,000 miles. None make funny noises (the newest is an 04 and its the only one that has a bit of piston slap when cold, not a problem at all, the noise goes away in 3 min and the noise never changes - shops try to tell me I have a problem, I keep away from these kind of shops). Even with high miles all my cars pass the strict California smog test with very low numbers.
We live in the part of Calif that gets snow - over 600 inches this year; hence the need for Subarus). The 3.3 in the SVX is an expanded 2.2 and the 2.2 can easily last 300,000 miles. I only use normal oil and I only change it every 7-8,000 miles. But I check it every week.
What leads people into thinking 100,000 miles is a lot? seriously, just do the water-pump-timing-belt every 100k and replace the starter, alternator and fuel pump at about 175 and thats about it. When the code says to replace an oxygen sensor do it right away.
Really: owning these is not a big costly proposition.
Very few modern engines (and everything since the "fuel injection transition year" of 1986 is in the "modern" catagory) are aywhere near worn out at 100,000.
You will not need an engine rebuild EVER because; if and when you do need an engine (just DO NOT ever run it without oil - that kills ALL engines), you will never need to rebuild it because there will always be an engine available from a wrecked car. Even with 150k miles a used engine with new oil seals (and a new pvc valve - it's a 3 dollar part) will be fine.
If you are worried about the engine lasting just make sure the oil level is OK and the radiator hoses are in good shape. Bad hoses cause far more engine deaths than anything else. Learn to read the check-engine-light codes yourself (it's easy). If you can do that owning this car will be a pleasure. Taking it to a shop to read the code leads to many unneeded repairs and alot of unneeded worry.
Good luck. Its a fun car.