One of my retail customers summed it up very well.
"The problem with .30-06 is it does everything so well." From 50gr Accelerator sabot loads (at over 4,000fps!!!) to 250gr thumpers, and everything in between.
IME all the .270s I've shot kick more than a comparable .30-06 rifle.
Feel like plinking? Get some old surplus .30 M1 or M2.
You can still get .30-06 in most small-town hardware stores across the country. Not always the case with .270 ammo.
"But the .270 shoots so flat!" So do .30 caliber bullets of the same weight. The .270 will have an edge in some arenas but not at typical hunting ranges. And if you're hunting big game at long(er) distances, those heavy .30-06 really start to shine!
The .270 is good if you want to sit around a campfire with younger folks, stroking each other about how great the .270 cartridge is.
If you are planning on world travel, chances are that you can find .30-06 in any place you are willing to travel. Teddy Roosevelt took ship loads of African game with .30-06 chambered rifles. And that was back before they REALLY got some interesting powder and bullet combinations going!
Carlos Hathcock used a .30-06 in a Winchester 70. What famous sniper used the .270 in what rifle?
Older service rifle shooters will tell you that the .308 shooters/protaganists had the rules changed to exclude .30-06 rifles back in the 1970s, "because they couldn't be beat by the lowly .308 cartridge."
While you may not get the distance and energy, you have a larger bullet selection with the .30-06 than you do with the .300 Win Mag, due to the latter cartridge's shorter neck interfering with seating longer bullets.
EVERYONE who makes rifle bullet moulds makes a variety of .309 and .310 diameter moulds in different shapes and contours.
On the other hand, the .270 is in the .30-06 family, so when you tire of it or regret your choice, you can neck up your used brass to use with your new .30-06 rifle (which you traded to the guy who just read all the ".270: King of The Cartridge" articles on old GUNS magazine articles.