Translating sentence of Luxun
I think your translation is mostly accurate. But I don't think 有 means "partly" directly. In Chinese, 有 usually means "there is/are". So a more "verbatim" translation would be

..., although there are merits in keeping the ancient tradition,...

with the following correspondence

虽=although

有=there are

功=merits

在于=in

怀古=keeping…

As for 思理, you may know that 思 means "think, thought", and 理 means "reason". So 思理朗然 means

with clear thinking and reasoning

or

the thinking and reasoning must be clear