I also wound up using initiator level-style scaling for Power of Cybernetics, which was my take on a sci-fi Incarnum. I doubt I'm the first to do that. I also had activator (meldshaper) level be a single value across an entire character, rather than be for each class, which neatly deals with the question of which number to use for non-class meldshaping abilities.
The good news about Incarnum's DCs is that they do get within 1 point of what you'd expect, assuming you're optimizing them with the standards. 4 essentia base + 2 from your class + 1 from the essentia capacity feat + 1 from an Incarnum Focus item means you get 8 essentia on your best soulmeld for a DC of 18 + Con, same as an 8th-level spell, except based on Constitution instead of Int, Wis, or Cha. Being Con-based means you get a lot of built-in benefits, and it's a bit easier to boost than most of the mental stats (although Soro's shown me that they're all a lot easier to improve than I think). This still has a few problems. You are actually spending a fair bit for that, even if it's also giving you strong benefits you'd want regardless. You don't have anywhere to go from there (possibly Ability Focus on your preferred soulmeld if that works, but otherwise there's no Spell Focus equivalent).
In regards to the effectiveness of the melds and their effects, that's a bit of a strange space. Some of them are really good. Numerical bonuses, at least, tend to be fine as-is. Damage for an essentia-optimized soulmeld can be rather high for the first few levels, although by 4th- or 5th-level they're just competing with (and eventually losing to) a Warlock, which is a terrible place to be. Adding an extra 6 essentia capacity over 20 levels will bring the damage up to semi-reasonable levels (although still dramatically weaker than spell-based blasting at mid-high levels). However, it does pump the numerical bonuses rather heavily, which may push thing further towards the edge of the d20 than you want.
Finally, any change to global essentia capacity likely necessitates a change to global essentia levels. You may need to adjust how much essentia each class and monster gets by levels, and you may need to rebalance the various feats, items, races, and other things grant.
For the numbers on essentia capacity, you may wish to round up instead of down. It makes for a smoother progression at low levels for non-meldshapers, who actually get nerfed in your version at level 7 where they'd normally improve to a capacity of 2. It also changes the progression for meldshapers to match Wizard spell levels.