Great engineers become much much more useful if you've secured the Mausoleum. Some (like Ada lovelace, the scourge of the industrial era) are still useless, but James Watt can give all your factories +4 production* and Tesla can make one uber factory/powerplant combo dish out 7 & 8 production over 12 tiles. Even Leo's workshops granting +2 culture is quite good. It's also handy to get an extra charge out of some wonder boosters. On the ocean side, the mausoleum is particularly handy if you get the Ironclad admiral- 2 ironclads very early is devastating on the coast.
*James Watt boosts the city's local yield, not the regional. The city will show the higher local yield, but others in range will still see the base +3 regional effect. Yes, this also means you can't combine watt and tesla to make a regional effect of +11 on a factory; locally yes, but regionally it will still only be +7. On the upside, it does give building factories some marginal benefit.
I'm really not sure why they let the mausoleum apply to engineers, since it's a balance nightmare.