1) In your Insights to Yoma 35:2, you question how the Afternoon Begadim can be added to -- doesn't the Gemara learn out that the morning Begadim have to be worth more?
You quote the answer of the Ritva who says that even though the afternoon Begadim can be added to, the morning Begadim still have to be more expensive.
But how will the Ritva explain the rule of the Gemara (and the examples) that the mothers of the Kohanim would make them clothes to do the "Avodas Yachid", which Rashi explains to mean removing the kaf from the Kodesh HaKodoshim -- isn't this itself the afternoon Avodah? The mothers would not be able to make special clothes for the morning service as it is not Avodat Yachid. So how could the Gemara allow it -- the afternoon clothes would be more than the morning clothes?
2) Also, perhaps another possible explanation of your question on the Rambam's shita who says there is no limitation of morning clothing being more expensive than afternoon -- is that we only learn from the pasuk about the Public money -- i.e. the morning clothing have to be more than the afternoon clothing as far as what may be used from Hekdesh -- but there is no limitation about private donations. The public ratio of the 18:12 may be changed to a minimum of 16:14 but no less. However, privately, much more can be added to the afternoon begadim. Since the Pasuk where Bad appears 4 times is written by the morning Avodah -- and in the morning Avodah which is Avodat Tzibur private donations would not be allowed, perhaps this Derasha requires the more expensive morning clothes only as far as the public money is concerned... The sevara for this might be simply that since the morning is Avodat Tzibbur the Torah considers it "more important", but the Torah does not limit the private Hidur of the Kohen at any time.
The mother of the Kohen made for him a linen garment for 20,000 Manah, how about the morning clothes , they would accordingly have to be more expensive than the evening or night garments causing the Tzibur more expenses than is necessary. The Gemarah does not discuss the consequences of allowing expensive garments for the evening and its impact on the morning garments.
According to the Girsa and explanation of the Me'iri (as cited by the Si'ach Yitzchak), the question does not begin, for he explains that the Gemara is not referring to any Avodah that was done on Yom Kipur. The Begadim contributed by the Kohen's mother were worn during the weekday, and not on Yom Kipur.
However, according to our Girsa and Rashi's explanation, your question is very strong. (According to Rashi's second explanation, that Avodas Yachid refers to reading the Torah, the question is not so strong, because the reading of the Torah did not have to be done in Bigdei Kehunah. However, there is another problem with that explanation -- if the reading of the Torah did not require Bigdei Kehunah, then why was it necessary to make sure that the donated Beged was given full-heartedly to the Tzibur? Rashi does not mention this problem as his reason for rejecting that explanation, and it is not clear why not. CHONEN DE'AH, p. 149, suggests an answer to this problem.)
The CHAFETZ CHAIM (in Zevach Todah) asks your question, and in fact he suggests the answer that Howie Schiffmiller suggests -- that the requirement for the morning Begadim to be worth more than the afternoon Begadim applies only for the money which the public gives; it is permitted to add from private funds to the afternoon Begadim even though as a result they will be worth more than the morning Begadim (see also Gevuras Ari, in his Milu'im on Maseches Yoma, 34b).
However, the Chafetz Chaim says that this answer is not satisfactory, because since the expensive Beged must be given over completely to the Tzibur, it becomes public funds and is considered as though the public gave it. The Chafetz Chaim therefore concludes with a question on Rashi's explanation, and sides with those Rishonim who learn that Avodas Yachid refers to normal days (such as when bringing private Korbanos) and not to Yom Kipur, and he brings proof to this from a Tosefta.
Others suggest differentiating between the change of clothing that was done solely for the Avodah of removing the Kaf u'Machtah, and the other changes of clothing that were done for all of the the other Avodos Tzibur. Since the removal of the Kaf u'Machtah was not an Avodah that was done on behalf of the Tzibur , as Rashi explains, the requirements that apply to the Begadim worn when doing Avodos on behalf of the Tzibur do not apply (see SEFER SHEMU'AS CHAIM, p. 422, and CHONEN DE'AH, p. 223). This is a very big Chidush though.
If anyone has any further thoughts on the matter, please share with us.