I think your glance is pretty accurate. To back it up with some math:
Egg tokens: 1000 sigils is the equivalent of ~5000 rubies in super sigil chests later in the season. Grinding 5000 rubies in egg missions will get you 15000 tokens, so twice this amount. Probably not worth it unless you expect to have a lot of left-over sigils. The value is still okay compared to getting them from any other line.
Timers: 400 sigils is ~2000 rubies in super sigil. That number of rubies will get you about 7 days in forge packs, or 5 days plus other stuff in gold chests. Even the timer-rich howitzer line has less timers per sigil over the whole line. 25 days for 400 sigils seems solid.
Embers 200 sigils is about 1000 rubies equivalent, which buys 2.5 gold chests. Those will drop 400 embers in fort, almost the same number, plus timers, sigils etc. Not worth it.
Rune Dust can’t really be calculated, since there isn’t really another source to buy it. Can be bad or good depending on your needs, it’s sure cheaper than getting a whole dragon line just for dust.
Gold Chests are a no-brainer to get. 20 chests will return 400 sigils on average, so you’re effectively paying 100 sigils for ~20 days of timers plus either 3200 embers or a bunch of pvp drops.