Almost all ticket types, if you are on an Avanti West Coast direct train to Liverpool, include a free seat reservation with the ticket anyway. So that is not a concern- or are you travelling on a Britrail pass or something similar?- in which case a reservation would certainly be advised.
If I was actually buying a ticket to Liverpool that weekend then Avanti have applied surge pricing by withdrawing all cheap Advance tickets. If it was me I would be putting myself to the minor inconvenience of changing trains at Crewe with "split ticketing". Take one Avanti train to Crewe on an Advance Ticket then change trains onto the Euston to Liverpool train buying an Off Peak Day Single. You will have seat reservations on both trains.
You can easily save £30 each by doing that- given what you will have paid for your hotels that is useful money.
If you take a slower London North Western train from Euston to Crewe (no seat reservations, but doesn't matter much on that leg) you can save as much as £50 each.