With the greatest respect, I do not agree that "apreciación pecuniaria" means valuable consideration here, and I think you were right in the first place: it doesn't fit this context. In fact I don't know what it means to speak of lawyers' fees not being subject to valuable consideration. "Valuable consideration" is a concept in contract law; it basically means payment for services rendered. Even if you see the lawyer-client relationship as contractual, the idea of the lawyer's fees being subject to valuable consideration is surely meaningless; those fees ARE valuable consideration for legal services rendered.

But in any case, "no susceptibles de apreciación pecuniaria" doesn't refer to "honorarios", the fees, but to "asuntos judiciales", the legal matters or types of cases in which those fees are paid. Whatever it means, it's a property of certain types of legal proceeding, the types listed: divorce, adoption, etc., not a property of the associated lawyers' fees.

So what does it mean? The following document is a helpful start:

"El juicio de cancelación de hipoteca no es susceptible de apreciación pecuniaria a los fines regulatorios porque con él sólo se pretende el levantamiento del gravamen hipotecario y no el cuestionamiento a la deuda garantizada. No existe pretensión de ningún beneficio patrimonial de una parte que se traslade a la otra. La regulación de honorarios debe efectuarse entonces teniendo en cuenta las disposiciones contenidas en los artículos 4 y 5 del Arancel."
http://www.jusonline.gov.ar/Jurisprudencia/textos.asp?id=947...

In other words, a case that is "no susceptible de apreciación pecuniaria" is one in which there is no monetary benefit to the winning party: the judgment doesn't involve any "beneficio patrimonial", any payment. In such cases, the lawyer gets a minimum set fee.

So what happens in the other kind of cases, those that are "susceptibles de apreciación pecuniaria", that is, those in which the winning party obtains a monetary benefit from the judgment? In that case, the lawyer gets a percentage of that monetary benefit, the "cuantía" or "monto" of the case. This is stated in the relevant law:

"En los procesos susceptibles de apreciación pecuniaria los honorarios por la defensa de cada una de las partes serán fijados según la cuantía de los mismos [i.e., of procesos of this kind], de acuerdo con la siguiente escala:

Escala..............................%
Hasta 15 UMA..................del 22% al 33%
De 16 UMA a 45 UMA.........del 20% al 26%
De 46 UMA a 90 UMA.........del 18% al 24%
De 91 UMA a 150 UMA.......del 17% al 22%
De 151 UMA a 450 UMA......del 15% al 20%
De 451 UMA a 750 UMA......del 13% al 17%
De 751 UMA en adelante.....del 12% al 15%
[...]
En el caso de los auxiliares de la Justicia, el monto de los honorarios a regular no podrá ser inferior al cinco por ciento (5%) ni superior al diez por ciento (10%) del monto del proceso."
https://ar.vlex.com/vid/ley-27-423-700000437?_ga=2.144474741...

So both lawyers and "auxiliares" get a percentage of the "monto del proceso", and that is defined here:

"El art. 19 de la ley 21.839 establece que se considerará monto del proceso la suma que resultare de la sentencia o transacción [...]"
https://www.pjn.gov.ar/Publicaciones/00002/00028663.Pdf

It's the amount awarded by the judgment: the amount the winning party gets. That, of course, doesn't apply to cases like divorce or adoption, where neither part gets a monetary award.

So I would suggest you might translate "asuntos judiciales no susceptibles de apreciación pecuniaria" as "non-monetary legal matters" or "cases". There may be a more suitable term, but I think it expresses the meaning.

"For this reason, we agree that a standard fee for all non-monetary cases is a sensible proposition."
https://consult.justice.gov.uk/digital-communications/court-...