Have you ever considered adding a skill system to the multi block system instead of purchasing them as advancements?
All players begin with a skill of 5% in all multi-blocks. You build the multi-block and click the sign. If your skill check fails the blocks explode. Less damage for lower level advancements, more for higher level advancements (more dangerous tech).
As you gain XP you can spend it on individual advancements. For having gained the XP you rank up player levels, which unlocks ships and you spend the XP to become better at making multi-blocks in the advancements of your choosing.
Tier I Power Bank skill requires a roll > 100 - (Power Bank Skill): at first this would be 95% chance of failure. You spend XP on Power Bank Skill to bring your chance of failure down.
Tier II Power Bank skill requires roll > 150 - (power Bank Skill)
Tier III Power Bank skill requires roll > 200 - (power Bank Skill)
Teir II and III would automatically be unattainable for low level players as to have even a small chance of success you would need a Power Bank Skill of at least 51 to have only a 1% chance of success at a Tier II build attempt.
In this scenario Skill are more like Knowledge, and no one person would be perfect at all skills.
As a sidebar this would add greater interest in scavenging wrecked ships because they might have complete active machines that could be towed away and added to ships or sold to other players.
This could create specialists in certain fields, especially at lower levels.
The success % doesn’t have to start out at 100, nor do beginning skill levels need to start at 5%, You’d need to decide what you want them to start at? It could also be that a failure would give that player a small chance at gaining a free level. This could turn into a grinding possibility so it would need to be capped at maybe 5 levels and 1 per purchased level or something,
Maybe when player begin the game they choose a profession which gives them bonuses in certain skills.
Scientist: +20 Gravity Well, + 20 Navigation Computers, + 10 Hyperdrives
Ship Engineer: +20 Thrusters, +20 Entrances, +10 Particle Shields
Miner: +20 Drills, +20 Power Banks, +10 Power Generators
Civil Engineer: +20 Base Shields, +20 Elevators, +10 Area Shields
(lots more professions required, player suggestion would be good)
As an alternative if a player wishes they could opt to distribute 40 skill levels into any skills of their choosing up to 20 in any one. They would gain 10 less skills and be considered a Rogue.