Which is hard for an upgrade for a gaggia owner, as I paid £100 for mine. To upgrade, as you say, I really would need to spend close to £1k! I don't think I'll ever do that, so I'll probably end up keeping the gaggia until it breaks (if it ever breaks, and can't be fixed).
best bet for a Gaggia upgrade is the grinder and adding a PID - stable temperature really helps. If you want a good machine but don't want to breach the £1k mark you can look at lever machines, a basic la pavoni europiccola is about £400 - it may not be an upgrade in stability (in terms of temp, pressure, repeatability) but you'll get better coffee from it - albeit one in every x shots